View source for Pell's equation

{{task|Mathematics}}

'''Pell's equation''' &nbsp; (also called the '''Pell–Fermat''' equation) &nbsp; is a &nbsp; [https://en.wikipedia.org/wiki/Diophantine_equation <u>Diophantine equation</u>] &nbsp; of the form:

:::::: <big> <b>  x<sup>2</sup> &nbsp; - &nbsp; ny<sup>2</sup> &nbsp; = &nbsp; 1  </b> </big>

with integer solutions for &nbsp; '''x''' &nbsp; and &nbsp; '''y''', &nbsp; where &nbsp; '''n''' &nbsp; is a given non-square positive integer.


;Task requirements:
:* &nbsp; find the smallest solution in positive integers to Pell's equation for &nbsp; '''n''' = {61, 109, 181, 277}.


;See also:
:* &nbsp; Wikipedia entry: [https://en.wikipedia.org/wiki/Pell%27s_equation <u>Pell's equation</u>].
<br><br>

=={{header|11l}}==
{{trans|Python}}

<syntaxhighlight lang="11l">F solvePell(n)
   V x = Int(sqrt(n))
   V (y, z, r) = (x, 1, x << 1)
   BigInt e1 = 1
   BigInt e2 = 0
   BigInt f1 = 0
   BigInt f2 = 1
   L
      y = r * z - y
      z = (n - y * y) I/ z
      r = (x + y) I/ z

      (e1, e2) = (e2, e1 + e2 * r)
      (f1, f2) = (f2, f1 + f2 * r)

      V (a, b) = (f2 * x + e2, f2)
      I a * a - n * b * b == 1
         R (a, b)

L(n) [61, 109, 181, 277]
   V (x, y) = solvePell(n)
   print(‘x^2 - #3 * y^2 = 1 for x = #27 and y = #25’.format(n, x, y))</syntaxhighlight>

{{out}}
<pre>
x^2 -  61 * y^2 = 1 for x =                  1766319049 and y =                 226153980
x^2 - 109 * y^2 = 1 for x =             158070671986249 and y =            15140424455100
x^2 - 181 * y^2 = 1 for x =         2469645423824185801 and y =        183567298683461940
x^2 - 277 * y^2 = 1 for x =       159150073798980475849 and y =       9562401173878027020
</pre>

=={{header|Ada}}==
{{Trans|C}}{{works with|Ada 2022}}
<syntaxhighlight lang="ada">with Ada.Text_Io;
with Ada.Numerics.Elementary_Functions;
with Ada.Numerics.Big_Numbers.Big_Integers;

procedure Pells_Equation is
   use Ada.Numerics.Big_Numbers.Big_Integers;

   type Pair is
      record
         V1, V2 : Big_Integer;
      end record;

   procedure Solve_Pell (N : Natural; X, Y : out Big_Integer) is
      use Ada.Numerics.Elementary_Functions;
      Big_N : constant Big_Integer := To_Big_Integer (N);
      XX    : constant Big_Integer := To_Big_Integer (Natural (Float'Floor (Sqrt (Float (N)))));
   begin
      if XX**2 = Big_N then
         X := 1; Y := 0;
         return;
      end if;

      declare
         YY   : Big_Integer := XX;
         Z    : Big_Integer := 1;
         R    : Big_Integer := 2 * XX;
         E    : Pair        := Pair'(V1 => 1, V2 => 0);
         F    : Pair        := Pair'(V1 => 0, V2 => 1);
      begin
         loop
            YY := R * Z - YY;
            Z  := (Big_N - YY**2) / Z;
            R  := (XX + YY) / Z;
            E  := Pair'(V1 => E.V2, V2 => R * E.V2 + E.V1);
            F  := Pair'(V1 => F.V2, V2 => R * F.V2 + F.V1);
            X  := E.V2 + XX * F.V2;
            Y  := F.V2;
            exit when X**2 - Big_N * Y**2 = 1;
         end loop;
      end;
   end Solve_Pell;

   procedure Test (N : Natural) is

      package Natural_Io is new Ada.Text_Io.Integer_Io (Natural);
      use Ada.Text_Io, Natural_Io;

      X, Y : Big_Integer;
   begin
      Solve_Pell (N, X => X, Y => Y);
      Put ("X**2 - ");
      Put (N, Width => 3);
      Put (" * Y**2 = 1 for X = ");
      Put (To_String (X, Width => 22));
      Put (" and Y = ");
      Put (To_String (Y, Width => 20));
      New_Line;
   end Test;

begin
   Test (61);
   Test (109);
   Test (181);
   Test (277);
end Pells_Equation;</syntaxhighlight>
{{out}}
<pre>
X**2 -  61 * Y**2 = 1 for X =             1766319049 and Y =            226153980
X**2 - 109 * Y**2 = 1 for X =        158070671986249 and Y =       15140424455100
X**2 - 181 * Y**2 = 1 for X =    2469645423824185801 and Y =   183567298683461940
X**2 - 277 * Y**2 = 1 for X =  159150073798980475849 and Y =  9562401173878027020
</pre>

=={{header|ALGOL 68}}==
{{Trans|Sidef}} Also tests for a trival solution only (if n is a perfect square only 1, 0 is solution).
{{works with|ALGOL 68G|Any - tested with release 2.8.3.win32}}
<syntaxhighlight lang="algol68">BEGIN
    # find solutions to Pell's eqauation: x^2 - ny^2 = 1 for integer x, y, n #
    MODE BIGINT     = LONG LONG INT;
    MODE BIGPAIR    = STRUCT( BIGINT v1, v2 );
    PROC solve pell = ( INT n )BIGPAIR:
         IF INT x = ENTIER( sqrt( n ) );
            x * x = n
         THEN
            # n is a erfect square - no solution otheg than 1,0              #
            BIGPAIR( 1, 0 )
         ELSE
            # there are non-trivial solutions                                #
            INT     y := x;
            INT     z := 1;
            INT     r := 2*x;
            BIGPAIR e := BIGPAIR( 1, 0 ); 
            BIGPAIR f := BIGPAIR( 0, 1 );
            BIGINT  a := 0;
            BIGINT  b := 0;
            WHILE
                y := (r*z - y);
                z := ENTIER ((n - y*y) / z);
                r := ENTIER ((x + y) / z);
                e := BIGPAIR( v2 OF e, r * v2 OF e + v1 OF e );
                f := BIGPAIR( v2 OF f, r * v2 OF f + v1 OF f );
                a := (v2 OF e + x*v2 OF f);
                b := v2 OF f;
                a*a - n*b*b /= 1
            DO SKIP OD;
            BIGPAIR( a, b )
         FI # solve pell # ;
    # task test cases                                                        #
    []INT nv = (61, 109, 181, 277);
    FOR i FROM LWB nv TO UPB nv DO
        INT  n = nv[ i ];
        BIGPAIR r = solve pell(n);
        print( ("x^2 - ", whole( n, -3 ), " * y^2 = 1 for x = ", whole( v1 OF r, -21), " and y = ", whole( v2 OF r, -21 ), newline ) )
    OD
END</syntaxhighlight>
{{out}}
<pre>
x^2 -  61 * y^2 = 1 for x =            1766319049 and y =             226153980
x^2 - 109 * y^2 = 1 for x =       158070671986249 and y =        15140424455100
x^2 - 181 * y^2 = 1 for x =   2469645423824185801 and y =    183567298683461940
x^2 - 277 * y^2 = 1 for x = 159150073798980475849 and y =   9562401173878027020
</pre>

=={{header|Arturo}}==
{{trans|Python}}

<syntaxhighlight lang="rebol">solvePell: function [n][
    x: to :integer sqrt n
    [y, z, r]: @[x, 1, shl x 1]
    [e1, e2]: [1, 0]
    [f1, f2]: [0, 1]

    while [true][
        y: (r * z) - y
        z: (n - y * y) / z
        r: (x + y) / z

        [e1, e2]: @[e2, e1 + e2 * r]
        [f1, f2]: @[f2, f1 + f2 * r]
        [a, b]: @[e2 + f2 * x, f2]
        if 1 = (a*a) - n*b*b -> 
            return @[a, b]
    ]
]

loop [61 109 181 277] 'n [
    [x, y]: solvePell n
    print ["x² -" n "* y² = 1 for (x,y) =" x "," y]
]</syntaxhighlight>

{{out}}

<pre>x² - 61 * y² = 1 for (x,y) = 1766319049 , 226153980 
x² - 109 * y² = 1 for (x,y) = 158070671986249 , 15140424455100 
x² - 181 * y² = 1 for (x,y) = 2469645423824185801 , 183567298683461940 
x² - 277 * y² = 1 for (x,y) = 159150073798980475849 , 9562401173878027020</pre>


=={{header|C}}==
{{trans|ALGOL 68}}
For n = 277, the x value is not correct because 64-bits is not enough to represent the value.
<syntaxhighlight lang="c">#include <math.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>

struct Pair {
    uint64_t v1, v2;
};

struct Pair makePair(uint64_t a, uint64_t b) {
    struct Pair r;
    r.v1 = a;
    r.v2 = b;
    return r;
}

struct Pair solvePell(int n) {
    int x = (int) sqrt(n);

    if (x * x == n) {
        // n is a perfect square - no solution other than 1,0
        return makePair(1, 0);
    } else {
        // there are non-trivial solutions
        int y = x;
        int z = 1;
        int r = 2 * x;
        struct Pair e = makePair(1, 0);
        struct Pair f = makePair(0, 1);
        uint64_t a = 0;
        uint64_t b = 0;

        while (true) {
            y = r * z - y;
            z = (n - y * y) / z;
            r = (x + y) / z;
            e = makePair(e.v2, r * e.v2 + e.v1);
            f = makePair(f.v2, r * f.v2 + f.v1);
            a = e.v2 + x * f.v2;
            b = f.v2;
            if (a * a - n * b * b == 1) {
                break;
            }
        }

        return makePair(a, b);
    }
}

void test(int n) {
    struct Pair r = solvePell(n);
    printf("x^2 - %3d * y^2 = 1 for x = %21llu and y = %21llu\n", n, r.v1, r.v2);
}

int main() {
    test(61);
    test(109);
    test(181);
    test(277);

    return 0;
}</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =            1766319049 and y =             226153980
x^2 - 109 * y^2 = 1 for x =       158070671986249 and y =        15140424455100
x^2 - 181 * y^2 = 1 for x =   2469645423824185801 and y =    183567298683461940
x^2 - 277 * y^2 = 1 for x =  11576121209304062921 and y =   9562401173878027020</pre>

=={{header|C++}}==
{{trans|C}}
As with the C solution, the output for n = 277 is not correct because 64-bits is not enough to represent the value. 
<syntaxhighlight lang="cpp">#include <iomanip>
#include <iostream>
#include <tuple>

std::tuple<uint64_t, uint64_t> solvePell(int n) {
    int x = (int)sqrt(n);

    if (x * x == n) {
        // n is a perfect square - no solution other than 1,0
        return std::make_pair(1, 0);
    }

    // there are non-trivial solutions
    int y = x;
    int z = 1;
    int r = 2 * x;
    std::tuple<uint64_t, uint64_t> e = std::make_pair(1, 0);
    std::tuple<uint64_t, uint64_t> f = std::make_pair(0, 1);
    uint64_t a = 0;
    uint64_t b = 0;

    while (true) {
        y = r * z - y;
        z = (n - y * y) / z;
        r = (x + y) / z;
        e = std::make_pair(std::get<1>(e), r * std::get<1>(e) + std::get<0>(e));
        f = std::make_pair(std::get<1>(f), r * std::get<1>(f) + std::get<0>(f));
        a = std::get<1>(e) + x * std::get<1>(f);
        b = std::get<1>(f);
        if (a * a - n * b * b == 1) {
            break;
        }
    }

    return std::make_pair(a, b);
}

void test(int n) {
    auto r = solvePell(n);
    std::cout << "x^2 - " << std::setw(3) << n << " * y^2 = 1 for x = " << std::setw(21) << std::get<0>(r) << " and y = " << std::setw(21) << std::get<1>(r) << '\n';
}

int main() {
    test(61);
    test(109);
    test(181);
    test(277);

    return 0;
}</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =            1766319049 and y =             226153980
x^2 - 109 * y^2 = 1 for x =       158070671986249 and y =        15140424455100
x^2 - 181 * y^2 = 1 for x =   2469645423824185801 and y =    183567298683461940
x^2 - 277 * y^2 = 1 for x =  11576121209304062921 and y =   9562401173878027020</pre>

=={{header|C sharp|C#}}==
{{trans|Sidef}}
<syntaxhighlight lang="csharp">using System;
using System.Numerics;

static class Program
{
    static void Fun(ref BigInteger a, ref BigInteger b, int c)
    {
        BigInteger t = a; a = b; b = b * c + t;
    }

    static void SolvePell(int n, ref BigInteger a, ref BigInteger b)
    {
        int x = (int)Math.Sqrt(n), y = x, z = 1, r = x << 1;
        BigInteger e1 = 1, e2 = 0, f1 = 0, f2 = 1;
        while (true)
        {
            y = r * z - y; z = (n - y * y) / z; r = (x + y) / z;
            Fun(ref e1, ref e2, r); Fun(ref f1, ref f2, r); a = f2; b = e2; Fun(ref b, ref a, x);
            if (a * a - n * b * b == 1) return;
        }
    }

    static void Main()
    {
        BigInteger x, y; foreach (int n in new[] { 61, 109, 181, 277 })
        {
            SolvePell(n, ref x, ref y);
            Console.WriteLine("x^2 - {0,3} * y^2 = 1 for x = {1,27:n0} and y = {2,25:n0}", n, x, y);
        }
    }
}</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =               1,766,319,049 and y =               226,153,980
x^2 - 109 * y^2 = 1 for x =         158,070,671,986,249 and y =        15,140,424,455,100
x^2 - 181 * y^2 = 1 for x =   2,469,645,423,824,185,801 and y =   183,567,298,683,461,940
x^2 - 277 * y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020</pre>

=={{header|D}}==
{{trans|C#}}
<syntaxhighlight lang="d">import std.bigint;
import std.math;
import std.stdio;

void fun(ref BigInt a, ref BigInt b, int c) {
    auto t = a;
    a = b;
    b = b * c + t;
}

void solvePell(int n, ref BigInt a, ref BigInt b) {
    int x = cast(int) sqrt(cast(real) n);
    int y = x;
    int z = 1;
    int r = x << 1;
    BigInt e1 = 1;
    BigInt e2 = 0;
    BigInt f1 = 0;
    BigInt f2 = 1;
    while (true) {
        y = r * z - y;
        z = (n - y * y) / z;
        r = (x + y) / z;
        fun(e1, e2, r);
        fun(f1, f2, r);
        a = f2;
        b = e2;
        fun(b, a, x);
        if (a * a - n * b * b == 1) {
            return;
        }
    }
}

void main() {
    BigInt x, y;
    foreach(n; [61, 109, 181, 277]) {
        solvePell(n, x, y);
        writefln("x^2 - %3d * y^2 = 1 for x = %27d and y = %25d", n, x, y);
    }
}</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =                  1766319049 and y =                 226153980
x^2 - 109 * y^2 = 1 for x =             158070671986249 and y =            15140424455100
x^2 - 181 * y^2 = 1 for x =         2469645423824185801 and y =        183567298683461940
x^2 - 277 * y^2 = 1 for x =       159150073798980475849 and y =       9562401173878027020</pre>
=={{header|Delphi}}==
{{libheader| System.SysUtils}}
{{libheader| Velthuis.BigIntegers}}
{{Trans|Go}}
<syntaxhighlight lang="delphi">
program Pells_equation;

{$APPTYPE CONSOLE}

uses
  System.SysUtils,
  Velthuis.BigIntegers;

type
  TPellResult = record
    x, y: BigInteger;
  end;

function SolvePell(nn: UInt64): TPellResult;
var
  n, x, y, z, r, e1, e2, f1,  t, u, a, b: BigInteger;
begin
  n := nn;
  x := nn;
  x := BigInteger.Sqrt(x);
  y := BigInteger(x);
  z := BigInteger.One;
  r := x shl 1;

  e1 := BigInteger.One;
  e2 := BigInteger.Zero;
  f1 := BigInteger.Zero;
  b := BigInteger.One;

  while True do
  begin
    y := (r * z) - y;
    z := (n - (y * y)) div z;
    r := (x + y) div z;

    u := BigInteger(e1);
    e1 := BigInteger(e2);
    e2 := (r * e2) + u;

    u := BigInteger(f1);
    f1 := BigInteger(b);

    b := r * b + u;
    a := e2 + x * b;

    t := (a * a) - (n * b * b);

    if t = 1 then
    begin
      with Result do
      begin
        x := BigInteger(a);
        y := BigInteger(b);
      end;
      Break;
    end;
  end;
end;

const
  ns: TArray<UInt64> = [61, 109, 181, 277];
  fmt = 'x^2 - %3d*y^2 = 1 for x = %-21s and y = %s';

begin
  for var n in ns do
    with SolvePell(n) do
      writeln(format(fmt, [n, x.ToString, y.ToString]));

  {$IFNDEF UNIX} readln; {$ENDIF}
end.</syntaxhighlight>

=={{header|Factor}}==
{{trans|Sidef}}
<syntaxhighlight lang="factor">USING: formatting kernel locals math math.functions sequences ;

:: solve-pell ( n -- a b )

    n sqrt >integer :> x!
    x :> y!
    1 :> z!
    2 x * :> r!

    1 0 :> ( e1! e2! )
    0 1 :> ( f1! f2! )
    0 0 :> ( a! b! )

    [ a sq b sq n * - 1 = ] [
        
        r z * y - y!
        n y sq - z / floor z!
        x y + z / floor r!

        e2 r e2 * e1 + e2! e1!
        f2 r f2 * f1 + f2! f1!

        e2 x f2 * + a!
        f2 b!

    ] until
    a b ;

{ 61 109 181 277 } [
    dup solve-pell
    "x^2 - %3d*y^2 = 1 for x = %-21d and y = %d\n" printf
] each</syntaxhighlight>
{{out}}
<pre>
x^2 -  61*y^2 = 1 for x = 1766319049            and y = 226153980
x^2 - 109*y^2 = 1 for x = 158070671986249       and y = 15140424455100
x^2 - 181*y^2 = 1 for x = 2469645423824185801   and y = 183567298683461940
x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|FreeBASIC}}==
{{trans|Visual Basic .NET}}
'''for n = 277 the result is wrong, I do not know if you can represent such large numbers in FreeBasic!'''
<syntaxhighlight lang="freebasic">
Sub Fun(Byref a As LongInt, Byref b As LongInt, c As Integer)
    Dim As LongInt t
    t = a : a = b : b = b * c + t
End Sub

Sub SolvePell(n As Integer, Byref a As LongInt, Byref b As LongInt)
    Dim As Integer z, r
    Dim As LongInt x, y, e1, e2, f1, f2
    x = Sqr(n) : y = x : z  = 1 : r  = 2 * x
    e1 = 1 : e2 = 0 : f1 = 0 : f2 = 1
    While True
        y = r * z - y : z = (n - y * y) / z : r = (x + y) / z
        Fun(e1, e2, r) : Fun(f1, f2, r) : a = f2 : b = e2 : Fun(b, a, x)
        If a * a - n * b * b = 1 Then Exit Sub
    Wend
End Sub

Dim As Integer i
Dim As LongInt x, y
Dim As Integer n(0 To 3) = {61, 109, 181, 277}
For i = 0 To 3 ''n In {61, 109, 181, 277}
    SolvePell(n(i), x, y)
    Print Using "x^2 - ### * y^2 = 1 for x = ##################### and y = #####################"; n(i); x; y
Next i 
</syntaxhighlight>
{{out}}
<pre>
x^2 -  61 * y^2 = 1 for x =            1766319049 and y =             226153980
x^2 - 109 * y^2 = 1 for x =       158070671986249 and y =        15140424455100
x^2 - 181 * y^2 = 1 for x =   2469645423824185801 and y =    183567298683461940
x^2 - 277 * y^2 = 1 for x =  -6870622864405488695 and y =  -8884342899831524596
</pre>
<math>Insert formula here</math>

=={{header|Go}}==
{{trans|Sidef}}
<syntaxhighlight lang="go">package main

import (
    "fmt"
    "math/big"
)

var big1 = new(big.Int).SetUint64(1)

func solvePell(nn uint64) (*big.Int, *big.Int) {
    n := new(big.Int).SetUint64(nn)
    x := new(big.Int).Set(n)
    x.Sqrt(x)
    y := new(big.Int).Set(x)
    z := new(big.Int).SetUint64(1)
    r := new(big.Int).Lsh(x, 1)

    e1 := new(big.Int).SetUint64(1)
    e2 := new(big.Int)
    f1 := new(big.Int)
    f2 := new(big.Int).SetUint64(1)

    t := new(big.Int)
    u := new(big.Int)
    a := new(big.Int)
    b := new(big.Int)
    for {
        t.Mul(r, z)
        y.Sub(t, y)
        t.Mul(y, y)
        t.Sub(n, t)
        z.Quo(t, z)
        t.Add(x, y)
        r.Quo(t, z)
        u.Set(e1)
        e1.Set(e2)
        t.Mul(r, e2)
        e2.Add(t, u)
        u.Set(f1)
        f1.Set(f2)
        t.Mul(r, f2)
        f2.Add(t, u)
        t.Mul(x, f2)
        a.Add(e2, t)
        b.Set(f2)
        t.Mul(a, a)
        u.Mul(n, b)
        u.Mul(u, b)
        t.Sub(t, u)
        if t.Cmp(big1) == 0 {
            return a, b
        }
    }
}

func main() {
    ns := []uint64{61, 109, 181, 277}
    for _, n := range ns {
        x, y := solvePell(n)
        fmt.Printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", n, x, y)
    }
}</syntaxhighlight>

{{out}}
<pre>
x^2 -  61*y^2 = 1 for x = 1766319049            and y = 226153980
x^2 - 109*y^2 = 1 for x = 158070671986249       and y = 15140424455100
x^2 - 181*y^2 = 1 for x = 2469645423824185801   and y = 183567298683461940
x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Haskell}}==
{{trans|Julia}}
<syntaxhighlight lang="haskell">pell :: Integer -> (Integer, Integer)
pell n = go (x, 1, x * 2, 1, 0, 0, 1)
  where
    x = floor $ sqrt $ fromIntegral n
    go (y, z, r, e1, e2, f1, f2) =
      let y' = r * z - y
          z' = (n - y' * y') `div` z
          r' = (x + y') `div` z'
          (e1', e2') = (e2, e2 * r' + e1)
          (f1', f2') = (f2, f2 * r' + f1)
          (a, b) = (f2', e2')
          (b', a') = (a, a * x + b)
      in if a' * a' - n * b' * b' == 1
         then (a', b')
         else go (y', z', r', e1', e2', f1', f2')</syntaxhighlight>

<pre>λ> mapM_ print $ pell <$> [61,109,181,277]
(1766319049,226153980)
(158070671986249,15140424455100)
(2469645423824185801,183567298683461940)
(159150073798980475849,9562401173878027020)</pre>

=={{header|J}}==

<syntaxhighlight lang="j">NB. sqrt representation for continued fraction
sqrt_cf =: 3 : 0
rep=. '' [ 'm d'=. 0 1 [ a =. a0=. <. %: y
while. a ~: +: a0 do.
  rep=. rep , a=. <. (a0+m) % d=. d %~ y - *: m=. m -~ a*d
end. a0;rep
)

NB. find x,y such that x^2 - n*y^2 = 1 using continued fractions 
pell =: 3 : 0
n =. 1 [ 'a0 as' =. x: &.> sqrt_cf y
while. 1 do. cs =. 2 x: (+%)/\ a0, n$as NB. convergents
  if. # sols =. I. 1 = (*: cs) +/ . * 1 , -y do. cs {~ {. sols return. end.
  n =. +: n
end.
)
</syntaxhighlight>

Check that task is actually solved
<syntaxhighlight lang="j">verify =: 3 : 0
assert. 1 = (*: xy) +/ . * 1 _61  [ echo 61  ; xy =. pell 61
assert. 1 = (*: xy) +/ . * 1 _109 [ echo 109 ; xy =. pell 109
assert. 1 = (*: xy) +/ . * 1 _181 [ echo 181 ; xy =. pell 181
assert. 1 = (*: xy) +/ . * 1 _277 [ echo 277 ; xy =. pell 277
)
</syntaxhighlight>
{{out}}
<pre>   verify ''
┌──┬────────────────────┐
│61│1766319049 226153980│
└──┴────────────────────┘
┌───┬──────────────────────────────┐
│109│158070671986249 15140424455100│
└───┴──────────────────────────────┘
┌───┬──────────────────────────────────────┐
│181│2469645423824185801 183567298683461940│
└───┴──────────────────────────────────────┘
┌───┬─────────────────────────────────────────┐
│277│159150073798980475849 9562401173878027020│
└───┴─────────────────────────────────────────┘
</pre>

=={{header|Java}}==
<syntaxhighlight lang="java">
import java.math.BigInteger;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.List;

public class PellsEquation {

    public static void main(String[] args) {
        NumberFormat format = NumberFormat.getInstance();
        for ( int n : new int[] {61, 109, 181, 277, 8941} ) {
            BigInteger[] pell = pellsEquation(n);
            System.out.printf("x^2 - %3d * y^2 = 1 for:%n    x = %s%n    y = %s%n%n", n,  format.format(pell[0]),  format.format(pell[1]));
        }
    }

    private static final BigInteger[] pellsEquation(int n) {
        int a0 = (int) Math.sqrt(n);
        if ( a0*a0 == n ) {
            throw new IllegalArgumentException("ERROR 102:  Invalid n = " + n);
        }
        List<Integer> continuedFrac = continuedFraction(n);
        int count = 0;
        BigInteger ajm2 = BigInteger.ONE;
        BigInteger ajm1 = new BigInteger(a0 + "");
        BigInteger bjm2 = BigInteger.ZERO;
        BigInteger bjm1 = BigInteger.ONE;
        boolean stop = (continuedFrac.size() % 2 == 1);
        if ( continuedFrac.size() == 2 ) {
            stop = true;
        }
        while ( true ) {
            count++;
            BigInteger bn = new BigInteger(continuedFrac.get(count) + "");
            BigInteger aj = bn.multiply(ajm1).add(ajm2);
            BigInteger bj = bn.multiply(bjm1).add(bjm2);
            if ( stop && (count == continuedFrac.size()-2 || continuedFrac.size() == 2) ) {
                return new BigInteger[] {aj, bj};
            }
            else if (continuedFrac.size() % 2 == 0 && count == continuedFrac.size()-2 ) {
                stop = true;
            }
            if ( count == continuedFrac.size()-1 ) {
                count = 0;
            }
            ajm2 = ajm1;
            ajm1 = aj;
            bjm2 = bjm1;
            bjm1 = bj;
        }
    }

    private static final List<Integer> continuedFraction(int n) {
        List<Integer> answer = new ArrayList<Integer>();
        int a0 = (int) Math.sqrt(n);
        answer.add(a0);
        int a = -a0;
        int aStart = a;
        int b = 1;
        int bStart = b;

        while ( true ) {
            //count++;
            int[] values = iterateFrac(n, a, b);
            answer.add(values[0]);
            a = values[1];
            b = values[2];
            if (a == aStart && b == bStart) break;
        }
        return answer;
    }
    
    //  array[0] = new part of cont frac
    //  array[1] = new a
    //  array[2] = new b
    private static final int[] iterateFrac(int n, int a, int b) {
        int x = (int) Math.floor((b * Math.sqrt(n) - b * a)/(n - a * a));
        int[] answer = new int[3];
        answer[0] = x;
        answer[1] = -(b * a + x *(n - a * a)) / b;
        answer[2] = (n - a * a) / b;
        return answer;
    }


}
</syntaxhighlight>

{{out}}
<pre>
x^2 -  61 * y^2 = 1 for:
    x = 1,766,319,049
    y = 226,153,980

x^2 - 109 * y^2 = 1 for:
    x = 158,070,671,986,249
    y = 15,140,424,455,100

x^2 - 181 * y^2 = 1 for:
    x = 2,469,645,423,824,185,801
    y = 183,567,298,683,461,940

x^2 - 277 * y^2 = 1 for:
    x = 159,150,073,798,980,475,849
    y = 9,562,401,173,878,027,020

x^2 - 8941 * y^2 = 1 for:
    x = 2,565,007,112,872,132,129,669,406,439,503,954,211,359,492,684,749,762,901,360,167,370,740,763,715,001,557,789,090,674,216,330,243,703,833,040,774,221,628,256,858,633,287,876,949,448,689,668,281,446,637,464,359,482,677,366,420,261,407,112,316,649,010,675,881,349,744,201
    y = 27,126,610,172,119,035,540,864,542,981,075,550,089,190,381,938,849,116,323,732,855,930,990,771,728,447,597,698,969,628,164,719,475,714,805,646,913,222,890,277,024,408,337,458,564,351,161,990,641,948,210,581,361,708,373,955,113,191,451,102,494,265,278,824,127,994,180
</pre>

=={{header|jq}}==
{{trans|Wren}}
'''Works with gojq, the Go implementation of jq'''

'''Preliminaries'''
<syntaxhighlight lang="jq"># If $j is 0, then an error condition is raised;
# otherwise, assuming infinite-precision integer arithmetic,
# if the input and $j are integers, then the result will be an integer.
def idivide($i; $j):
  ($i % $j) as $mod
  | ($i - $mod) / $j ;
def idivide($j):
  idivide(.; $j);

# input should be a non-negative integer for accuracy
# but may be any non-negative finite number
def isqrt:
  def irt:
  . as $x
    | 1 | until(. > $x; . * 4) as $q
    | {$q, $x, r: 0}
    | until( .q <= 1;
        .q |= idivide(4)
        | .t = .x - .r - .q
        | .r |= idivide(2)
        | if .t >= 0
          then .x = .t
          | .r += .q
          else .
          end)
    | .r ;
  if type == "number" and (isinfinite|not) and (isnan|not) and . >= 0
  then irt
  else "isqrt requires a non-negative integer for accuracy" | error
  end ;</syntaxhighlight>
'''The Task'''
<syntaxhighlight lang="jq">def solvePell:
  . as $n
  | ($n|isqrt) as $x
  | { $x,
     y : $x,
     z : 1,
     r : ($x * 2),
     v1 : 1,
     v2 : 0,
     f1 : 0,
     f2 : 1 }
  | until(.emit;
      .y = .r*.z - .y
      | .z = idivide($n - .y*.y; .z)
      | .r = idivide(.x + .y; .z)
      | .v1 as $t
      | .v1 = .v2
      | .v2 = .r*.v2 + $t
      | .f1 as $t
      | .f1 = .f2
      | .f2 = .r*.f2 + $t
      | (.v2 + .x*.f2) as $a
      | .f2 as $b
      | if ($a*$a - $n*$b*$b == 1) then .emit = [$a, $b] else . end
    ).emit ;
 
(61, 109, 181, 277)
| solvePell as $res
| "x² - \(.)y² = 1 for x = \($res[0]) and y = \($res[1])"</syntaxhighlight>
{{out}}
<pre>
x² - 61y² = 1 for x = 1766319049 and y = 226153980
x² - 109y² = 1 for x = 158070671986249 and y = 15140424455100
x² - 181y² = 1 for x = 2469645423824185801 and y = 183567298683461940
x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Julia}}==
{{trans|C#}}
<syntaxhighlight lang="julia">function pell(n)
    x = BigInt(floor(sqrt(n)))
    y, z, r = x, BigInt(1), x << 1
    e1, e2, f1, f2 = BigInt(1), BigInt(0), BigInt(0), BigInt(1)
    while true
        y = r * z - y
        z = div(n - y * y, z)
        r = div(x + y, z)
        e1, e2 = e2, e2 * r + e1
        f1, f2 = f2, f2 * r + f1
        a, b = f2, e2
        b, a = a, a * x + b
        if a * a - n * b * b == 1
            return a, b
        end
    end
end

for target in BigInt[61, 109, 181, 277]
    x, y = pell(target)
    println("x\u00b2 - $target", "y\u00b2 = 1 for x = $x and y = $y")
end
</syntaxhighlight>{{out}}
<pre>
x² - 61y² = 1 for x = 1766319049 and y = 226153980
x² - 109y² = 1 for x = 158070671986249 and y = 15140424455100
x² - 181y² = 1 for x = 2469645423824185801 and y = 183567298683461940
x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Kotlin}}==
{{trans|C#}}
<syntaxhighlight lang="scala">import java.math.BigInteger
import kotlin.math.sqrt

class BIRef(var value: BigInteger) {
    operator fun minus(b: BIRef): BIRef {
        return BIRef(value - b.value)
    }

    operator fun times(b: BIRef): BIRef {
        return BIRef(value * b.value)
    }

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (javaClass != other?.javaClass) return false

        other as BIRef

        if (value != other.value) return false

        return true
    }

    override fun hashCode(): Int {
        return value.hashCode()
    }

    override fun toString(): String {
        return value.toString()
    }
}

fun f(a: BIRef, b: BIRef, c: Int) {
    val t = a.value
    a.value = b.value
    b.value = b.value * BigInteger.valueOf(c.toLong()) + t
}

fun solvePell(n: Int, a: BIRef, b: BIRef) {
    val x = sqrt(n.toDouble()).toInt()
    var y = x
    var z = 1
    var r = x shl 1
    val e1 = BIRef(BigInteger.ONE)
    val e2 = BIRef(BigInteger.ZERO)
    val f1 = BIRef(BigInteger.ZERO)
    val f2 = BIRef(BigInteger.ONE)
    while (true) {
        y = r * z - y
        z = (n - y * y) / z
        r = (x + y) / z
        f(e1, e2, r)
        f(f1, f2, r)
        a.value = f2.value
        b.value = e2.value
        f(b, a, x)
        if (a * a - BIRef(n.toBigInteger()) * b * b == BIRef(BigInteger.ONE)) {
            return
        }
    }
}

fun main() {
    val x = BIRef(BigInteger.ZERO)
    val y = BIRef(BigInteger.ZERO)
    intArrayOf(61, 109, 181, 277).forEach {
        solvePell(it, x, y)
        println("x^2 - %3d * y^2 = 1 for x = %,27d and y = %,25d".format(it, x.value, y.value))
    }
}</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =               1,766,319,049 and y =               226,153,980
x^2 - 109 * y^2 = 1 for x =         158,070,671,986,249 and y =        15,140,424,455,100
x^2 - 181 * y^2 = 1 for x =   2,469,645,423,824,185,801 and y =   183,567,298,683,461,940
x^2 - 277 * y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020</pre>

=={{header|Lambdatalk}}==
Computing big numbers requires the lib_BN library.
<syntaxhighlight lang="Scheme">
{def pell
 {lambda {:n}
  {let { {:n :n}
         {:x {BN.intPart {BN.sqrt :n}}}               // x=int(sqrt(n))
       } {pell.r :n :x :x 1 {* 2 :x} 1 0 0 1}
}}} 
-> pell

{def pell.r
 {lambda {:n :x :y :z :r :e1 :e2 :f1 :f2}
  {let { {:n :n} {:x :x} {:z :z} {:r :r}              // no closure ->
         {:e1 :e1} {:e2 :e2} {:f1 :f1} {:f2 :f2}      // must reassign :(
         {:y {BN.- {BN.* :r :z} :y}}                  // y=rz-y        
  } {let { {:n :n} {:x :x} {:y :y} {:r :r}
           {:e1 :e1} {:e2 :e2} {:f1 :f1} {:f2 :f2}
           {:z {BN.intPart
                {BN./ {BN.- :n {BN.* :y :y}} :z}}}    // z=(n-y*y)//z                                
   } {let { {:n :n} {:x :x} {:y :y} {:z :z}
            {:e1 :e1} {:e2 :e2} {:f1 :f1} {:f2 :f2}  
            {:r {BN.intPart {BN./ {BN.+ :x :y} :z}}}  // r= (x+y)//z                              
    } {let { {:n :n} {:x :x} {:y :y} {:z :z} {:r :r}
             {:e1 :e2}                                // e1=e2
             {:e2 {BN.+ {BN.* :r :e2} :e1}}           // e2=r*e2+e1
             {:f1 :f2}                                // f1=f2
             {:f2 {BN.+ {BN.* :r :f2} :f1}}           // f2=r*f2+f1       
     } {let { {:n :n} {:x :x} {:y :y} {:z :z} {:r :r}
              {:e1 :e1} {:e2 :e2} {:f1 :f1} {:f2 :f2}    
              {:a {BN.+ :e2 {BN.* :x :f2}}}           // a=e2+x*f2
              {:b :f2}                                // b=f2
      } {if {= {BN.compare {BN.- {BN.* :a :a}   
                                 {BN.* :n {BN.* :b :b}}}
                           1}
               0}                                     // a*a-n*b*b == 1
        then {div}x{sup 2} - n*y{sup 2} = 1 for n=:n, x=:a, y=:b 
        else {pell.r :n :x :y :z :r :e1 :e2 :f1 :f2}  // do it again
}}}}}}}} 
-> pell.r
 
{S.map pell 61 109 181 277}
->
x^2 - n*y^2 = 1 for n=61, x=1766319049, y=226153980 
x^2 - n*y^2 = 1 for n=109, x=158070671986249, y=15140424455100 
x^2 - n*y^2 = 1 for n=181, x=2469645423824185801, y=183567298683461940 
x^2 - n*y^2 = 1 for n=277, x=159150073798980475849, y=9562401173878027020
</syntaxhighlight>

=={{header|langur}}==
{{trans|D}}
<syntaxhighlight lang="langur">val .fun = fn(.a, .b, .c) { [.b, .b * .c + .a] }

val .solvePell = fn(.n) {
    val .x = trunc .n ^/ 2
    var .y, .z, .r = .x, 1, .x * 2
    var .e1, .e2, .f1, .f2 = 1, 0, 0, 1

    for {
        .y = .r * .z - .y
        .z = (.n - .y * .y) \ .z
        .r = (.x + .y) \ .z
        .e1, .e2 = .fun(.e1, .e2, .r)
        .f1, .f2 = .fun(.f1, .f2, .r)
        val .b, .a = .fun(.e2, .f2, .x)
        if .a^2 - .n * .b^2 == 1: return [.a, .b]
    }
}

val .C = fn(.x) {
    # format number string with commas
    var .neg, .s = "", string .x
    if .s[1] == '-' {
        .neg, .s = "-", rest .s
    }
    .neg ~ join ",", split -3, .s
}

for .n in [61, 109, 181, 277, 8941] {
    val .x, .y = .solvePell(.n)
    writeln $"x² - \.n;y² = 1 for:\n\tx = \.x:fn C;\n\ty = \.y:fn C;\n"
}
</syntaxhighlight>

{{out}}
<pre>x² - 61y² = 1 for:
	x = 1,766,319,049
	y = 226,153,980

x² - 109y² = 1 for:
	x = 158,070,671,986,249
	y = 15,140,424,455,100

x² - 181y² = 1 for:
	x = 2,469,645,423,824,185,801
	y = 183,567,298,683,461,940

x² - 277y² = 1 for:
	x = 159,150,073,798,980,475,849
	y = 9,562,401,173,878,027,020

x² - 8941y² = 1 for:
	x = 2,565,007,112,872,132,129,669,406,439,503,954,211,359,492,684,749,762,901,360,167,370,740,763,715,001,557,789,090,674,216,330,243,703,833,040,774,221,628,256,858,633,287,876,949,448,689,668,281,446,637,464,359,482,677,366,420,261,407,112,316,649,010,675,881,349,744,201
	y = 27,126,610,172,119,035,540,864,542,981,075,550,089,190,381,938,849,116,323,732,855,930,990,771,728,447,597,698,969,628,164,719,475,714,805,646,913,222,890,277,024,408,337,458,564,351,161,990,641,948,210,581,361,708,373,955,113,191,451,102,494,265,278,824,127,994,180
</pre>

=={{header|Mathematica}}/{{header|Wolfram Language}}==
<syntaxhighlight lang="mathematica">FindInstance[x^2 - 61 y^2 == 1, {x, y}, PositiveIntegers]
FindInstance[x^2 - 109 y^2 == 1, {x, y}, PositiveIntegers]
FindInstance[x^2 - 181 y^2 == 1, {x, y}, PositiveIntegers]
FindInstance[x^2 - 277 y^2 == 1, {x, y}, PositiveIntegers]</syntaxhighlight>
{{out}}
<pre>{{x -> 1766319049, y -> 226153980}}
{{x -> 158070671986249, y -> 15140424455100}}
{{x -> 2469645423824185801, y -> 183567298683461940}}
{{x -> 159150073798980475849, y -> 9562401173878027020}}</pre>

=={{header|Nim}}==
{{trans|Python}}
{{libheader|bignum}}
<syntaxhighlight lang="nim">import math, strformat
import bignum

func solvePell(n: int): (Int, Int) =
  let x = newInt(sqrt(n.toFloat).int)
  var (y, z, r) = (x, newInt(1), x shl 1)
  var (e1, e2) = (newInt(1), newInt(0))
  var (f1, f2) = (newInt(0), newInt(1))

  while true:
    y = r * z - y
    z = (n - y * y) div z
    r = (x + y) div z

    (e1, e2) = (e2, e1 + e2 * r)
    (f1, f2) = (f2, f1 + f2 * r)

    let (a, b) = (f2 * x + e2, f2)
    if a * a - n * b * b == 1:
      return (a, b)

for n in [61, 109, 181, 277]:
  let (x, y) = solvePell(n)
  echo &"x² - {n:3} * y² = 1 for (x, y) = ({x:>21}, {y:>19})"</syntaxhighlight>

{{out}}
<pre>x² -  61 * y² = 1 for (x, y) = (           1766319049,           226153980)
x² - 109 * y² = 1 for (x, y) = (      158070671986249,      15140424455100)
x² - 181 * y² = 1 for (x, y) = (  2469645423824185801,  183567298683461940)
x² - 277 * y² = 1 for (x, y) = (159150073798980475849, 9562401173878027020)</pre>

=={{header|Pascal}}==
{{libheader|IntXLib4Pascal}}
A console application in Free Pascal, created with the Lazarus IDE.

Pascal has no built-in support for arbitrarily large integers. The program below requires integers larger than 64 bits, and therefore uses an external library. The code could easily be adapted to solve the negative Pell equation x^2 - n*y^2 = -1, or show that no solution exists.
<syntaxhighlight lang="pascal">
program Pell_console;
uses SysUtils,
     uIntX; // uIntX is a unit in the library IntXLib4Pascal.
            // uIntX.TIntX is an arbitrarily large integer.

// For the given n: if there are non-trivial solutions of x^2 - n*y^2 = 1
//   in non-negative integers (x,y), return the smallest.
// Else return the trivial solution (x,y) = (1,0).
procedure SolvePell( n : integer; out x, y : uIntX.TIntX);
var
  m, a, c, d : integer;
  p, q, p_next, q_next, p_prev, q_prev : uIntX.TIntX;
  evenNrSteps : boolean;
begin
  if (n >= 0) then m := Trunc( Sqrt( 1.0*n + 0.5)) // or use Rosetta Code Isqrt
              else m := 0;
  if n <= m*m then begin    // if n is not a positive non-square
    x := 1;  y := 0;  exit; // return a trivial solution
  end;
  c := m;  d := 1;
  p := 1;  q := 0;
  p_prev := 0;  q_prev := 1;
  a := m;
  evenNrSteps := true;
  repeat
    // Get the next convergent p/q in the continued fraction for sqrt(n)
    p_next := a*p + p_prev;
    q_next := a*q + q_prev;
    p_prev := p;  p := p_next;
    q_prev := q;  q := q_next;
    // Get the next term a in the continued fraction for sqrt(n)
    Assert((n - c*c) mod d = 0); // optional sanity check
    d := (n - c*c) div d;
    a := (m + c) div d;
    c := a*d - c;
    evenNrSteps := not evenNrSteps;
  until (c = m) and (d = 1);
{
  If the first return to (c,d) = (m,1) occurs after an even number of steps,
    then p^2 - n*q^2 = 1, and there is no solution to x^2 - n*y^2 = -1.
  Else p^2 - n*q^2 = -1, and to get a solution to x^2 - n*y^2 = 1 we can
    either continue until we return to (c,d) = (m,1) for the second time,
    or use the short cut below.
}
  if evenNrSteps then begin
    x := p;  y := q;
  end
  else begin
    x := 2*p*p + 1;  y := 2*p*q
  end;
end;

// For the given n: show the Pell solution on the console.
procedure ShowPellSolution( n : integer);
var
  x, y : uIntX.TIntX;
  lineOut : string;
begin
  SolvePell( n, x, y);
  lineOut := SysUtils.Format( 'n = %d --> (', [n]);
  lineOut := lineOut + x.ToString + ', ' + y.ToString + ')';
  WriteLn( lineOut);
end;

// Main routine
begin
    ShowPellSolution( 61);
    ShowPellSolution( 109);
    ShowPellSolution( 181);
    ShowPellSolution( 277);
end.
</syntaxhighlight>
{{out}}
<pre>
n = 61 --> (1766319049, 226153980)
n = 109 --> (158070671986249, 15140424455100)
n = 181 --> (2469645423824185801, 183567298683461940)
n = 277 --> (159150073798980475849, 9562401173878027020)
</pre>

=={{header|Perl}}==
<syntaxhighlight lang="perl">sub solve_pell {
    my ($n) = @_;

    use bigint try => 'GMP';

    my $x = int(sqrt($n));
    my $y = $x;
    my $z = 1;
    my $r = 2 * $x;

    my ($e1, $e2) = (1, 0);
    my ($f1, $f2) = (0, 1);

    for (; ;) {

        $y = $r * $z - $y;
        $z = int(($n - $y * $y) / $z);
        $r = int(($x + $y) / $z);

        ($e1, $e2) = ($e2, $r * $e2 + $e1);
        ($f1, $f2) = ($f2, $r * $f2 + $f1);

        my $A = $e2 + $x * $f2;
        my $B = $f2;

        if ($A**2 - $n * $B**2 == 1) {
            return ($A, $B);
        }
    }
}

foreach my $n (61, 109, 181, 277) {
    my ($x, $y) = solve_pell($n);
    printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", $n, $x, $y);
}</syntaxhighlight>
{{out}}
<pre>
x^2 -  61*y^2 = 1 for x = 1766319049            and y = 226153980
x^2 - 109*y^2 = 1 for x = 158070671986249       and y = 15140424455100
x^2 - 181*y^2 = 1 for x = 2469645423824185801   and y = 183567298683461940
x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Phix}}==
{{trans|C#}}
{{trans|Go}}
{{libheader|Phix/mpfr}}
This now ignores the nonsquare part of the task spec, returning {1,0}.
<!--<syntaxhighlight lang="phix">(phixonline)-->
 <span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
 
 <span style="color: #008080;">include</span> <span style="color: #7060A8;">mpfr</span><span style="color: #0000FF;">.</span><span style="color: #000000;">e</span>
  
 <span style="color: #008080;">procedure</span> <span style="color: #000000;">fun</span><span style="color: #0000FF;">(</span><span style="color: #004080;">mpz</span> <span style="color: #000000;">a</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span> <span style="color: #004080;">integer</span> <span style="color: #000000;">c</span><span style="color: #0000FF;">)</span>
 <span style="color: #000080;font-style:italic;">-- {a,b} = {b,c*b+a}  (and t gets trashed)</span>
     <span style="color: #7060A8;">mpz_set</span><span style="color: #0000FF;">(</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">a</span><span style="color: #0000FF;">)</span>
     <span style="color: #7060A8;">mpz_set</span><span style="color: #0000FF;">(</span><span style="color: #000000;">a</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">)</span>
     <span style="color: #7060A8;">mpz_mul_si</span><span style="color: #0000FF;">(</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">c</span><span style="color: #0000FF;">)</span>
     <span style="color: #7060A8;">mpz_add</span><span style="color: #0000FF;">(</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
  
 <span style="color: #008080;">function</span> <span style="color: #000000;">SolvePell</span><span style="color: #0000FF;">(</span><span style="color: #004080;">integer</span> <span style="color: #000000;">n</span><span style="color: #0000FF;">)</span>
 <span style="color: #004080;">integer</span> <span style="color: #000000;">x</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">floor</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">sqrt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">n</span><span style="color: #0000FF;">)),</span> <span style="color: #000000;">y</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">z</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">r</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">*</span><span style="color: #000000;">2</span>
 <span style="color: #004080;">mpz</span> <span style="color: #000000;">e1</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span> <span style="color: #000000;">e2</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(),</span> 
     <span style="color: #000000;">f1</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(),</span>  <span style="color: #000000;">f2</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span>
     <span style="color: #000000;">t</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">),</span>   <span style="color: #000000;">u</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(),</span>
     <span style="color: #000000;">a</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span>   <span style="color: #000000;">b</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_init</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">)</span>
     <span style="color: #008080;">if</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">*</span><span style="color: #000000;">x</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">n</span> <span style="color: #008080;">then</span> 
         <span style="color: #008080;">while</span> <span style="color: #7060A8;">mpz_cmp_si</span><span style="color: #0000FF;">(</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)!=</span><span style="color: #000000;">0</span> <span style="color: #008080;">do</span>
             <span style="color: #000000;">y</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">r</span><span style="color: #0000FF;">*</span><span style="color: #000000;">z</span> <span style="color: #0000FF;">-</span> <span style="color: #000000;">y</span>
             <span style="color: #000000;">z</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">floor</span><span style="color: #0000FF;">((</span><span style="color: #000000;">n</span><span style="color: #0000FF;">-</span><span style="color: #000000;">y</span><span style="color: #0000FF;">*</span><span style="color: #000000;">y</span><span style="color: #0000FF;">)/</span><span style="color: #000000;">z</span><span style="color: #0000FF;">)</span>
             <span style="color: #000000;">r</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">floor</span><span style="color: #0000FF;">((</span><span style="color: #000000;">x</span><span style="color: #0000FF;">+</span><span style="color: #000000;">y</span><span style="color: #0000FF;">)/</span><span style="color: #000000;">z</span><span style="color: #0000FF;">)</span>
             <span style="color: #000000;">fun</span><span style="color: #0000FF;">(</span><span style="color: #000000;">e1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">e2</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">r</span><span style="color: #0000FF;">)</span>          <span style="color: #000080;font-style:italic;">-- {e1,e2} = {e2,r*e2+e1}</span>
             <span style="color: #000000;">fun</span><span style="color: #0000FF;">(</span><span style="color: #000000;">f1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">f2</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">r</span><span style="color: #0000FF;">)</span>          <span style="color: #000080;font-style:italic;">-- {f1,f2} = {f2,r*r2+f1}</span>
             <span style="color: #7060A8;">mpz_set</span><span style="color: #0000FF;">(</span><span style="color: #000000;">a</span><span style="color: #0000FF;">,</span><span style="color: #000000;">f2</span><span style="color: #0000FF;">)</span>
             <span style="color: #7060A8;">mpz_set</span><span style="color: #0000FF;">(</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">e2</span><span style="color: #0000FF;">)</span>
             <span style="color: #000000;">fun</span><span style="color: #0000FF;">(</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">a</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">x</span><span style="color: #0000FF;">)</span>            <span style="color: #000080;font-style:italic;">-- {b,a} = {f2,x*f2+e2}</span>
             <span style="color: #7060A8;">mpz_mul</span><span style="color: #0000FF;">(</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">a</span><span style="color: #0000FF;">,</span><span style="color: #000000;">a</span><span style="color: #0000FF;">)</span>
             <span style="color: #7060A8;">mpz_mul_si</span><span style="color: #0000FF;">(</span><span style="color: #000000;">u</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">,</span><span style="color: #000000;">n</span><span style="color: #0000FF;">)</span>
             <span style="color: #7060A8;">mpz_mul</span><span style="color: #0000FF;">(</span><span style="color: #000000;">u</span><span style="color: #0000FF;">,</span><span style="color: #000000;">u</span><span style="color: #0000FF;">,</span><span style="color: #000000;">b</span><span style="color: #0000FF;">)</span>
             <span style="color: #7060A8;">mpz_sub</span><span style="color: #0000FF;">(</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">t</span><span style="color: #0000FF;">,</span><span style="color: #000000;">u</span><span style="color: #0000FF;">)</span>          <span style="color: #000080;font-style:italic;">-- t = a^2-n*b^2</span>
         <span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
     <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
     <span style="color: #008080;">return</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">a</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">b</span><span style="color: #0000FF;">}</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
 
 <span style="color: #008080;">function</span> <span style="color: #000000;">split_into_chunks</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">,</span> <span style="color: #004080;">integer</span> <span style="color: #000000;">one</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">rest</span><span style="color: #0000FF;">)</span>
     <span style="color: #004080;">sequence</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..</span><span style="color: #000000;">one</span><span style="color: #0000FF;">]}</span>
     <span style="color: #000000;">x</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">one</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..$]</span>
     <span style="color: #004080;">integer</span> <span style="color: #000000;">l</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">)</span>
     <span style="color: #008080;">while</span> <span style="color: #000000;">l</span> <span style="color: #008080;">do</span>
         <span style="color: #004080;">integer</span> <span style="color: #000000;">k</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">min</span><span style="color: #0000FF;">(</span><span style="color: #000000;">l</span><span style="color: #0000FF;">,</span><span style="color: #000000;">rest</span><span style="color: #0000FF;">)</span>
         <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..</span><span style="color: #000000;">k</span><span style="color: #0000FF;">])</span>
         <span style="color: #000000;">x</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">[</span><span style="color: #000000;">k</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..$]</span>
         <span style="color: #000000;">l</span> <span style="color: #0000FF;">-=</span> <span style="color: #000000;">k</span>
     <span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
     <span style="color: #008080;">return</span> <span style="color: #7060A8;">join</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"\n"</span><span style="color: #0000FF;">&</span><span style="color: #7060A8;">repeat</span><span style="color: #0000FF;">(</span><span style="color: #008000;">' '</span><span style="color: #0000FF;">,</span><span style="color: #000000;">29</span><span style="color: #0000FF;">))&</span><span style="color: #008000;">"\n"</span><span style="color: #0000FF;">&</span><span style="color: #7060A8;">repeat</span><span style="color: #0000FF;">(</span><span style="color: #008000;">' '</span><span style="color: #0000FF;">,</span><span style="color: #000000;">17</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
 
 <span style="color: #004080;">sequence</span> <span style="color: #000000;">ns</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">4</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">61</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">109</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">181</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">277</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">8941</span><span style="color: #0000FF;">}</span>
 <span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ns</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
     <span style="color: #004080;">integer</span> <span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ns</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span>
     <span style="color: #004080;">mpz</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">x</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">y</span><span style="color: #0000FF;">}</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">SolvePell</span><span style="color: #0000FF;">(</span><span style="color: #000000;">n</span><span style="color: #0000FF;">)</span>
     <span style="color: #004080;">string</span> <span style="color: #000000;">xs</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_get_str</span><span style="color: #0000FF;">(</span><span style="color: #000000;">x</span><span style="color: #0000FF;">,</span><span style="color: #000000;">comma_fill</span><span style="color: #0000FF;">:=</span><span style="color: #004600;">true</span><span style="color: #0000FF;">),</span>
            <span style="color: #000000;">ys</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">mpz_get_str</span><span style="color: #0000FF;">(</span><span style="color: #000000;">y</span><span style="color: #0000FF;">,</span><span style="color: #000000;">comma_fill</span><span style="color: #0000FF;">:=</span><span style="color: #004600;">true</span><span style="color: #0000FF;">)</span>
     <span style="color: #008080;">if</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">xs</span><span style="color: #0000FF;">)></span><span style="color: #000000;">97</span> <span style="color: #008080;">then</span>
         <span style="color: #000000;">xs</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">split_into_chunks</span><span style="color: #0000FF;">(</span><span style="color: #000000;">xs</span><span style="color: #0000FF;">,</span><span style="color: #000000;">98</span><span style="color: #0000FF;">,</span><span style="color: #000000;">96</span><span style="color: #0000FF;">)</span>
         <span style="color: #000000;">ys</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">split_into_chunks</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ys</span><span style="color: #0000FF;">,</span><span style="color: #000000;">99</span><span style="color: #0000FF;">,</span><span style="color: #000000;">96</span><span style="color: #0000FF;">)</span>
     <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
     <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"x^2 - %3d*y^2 = 1 for x = %27s and y = %25s\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">n</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">xs</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">ys</span><span style="color: #0000FF;">})</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<!--</syntaxhighlight>-->
{{out}}
<pre>
x^2 -   4*y^2 = 1 for x =                           1 and y =                         0
x^2 -  61*y^2 = 1 for x =               1,766,319,049 and y =               226,153,980
x^2 - 109*y^2 = 1 for x =         158,070,671,986,249 and y =        15,140,424,455,100
x^2 - 181*y^2 = 1 for x =   2,469,645,423,824,185,801 and y =   183,567,298,683,461,940
x^2 - 277*y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020
x^2 - 8941*y^2 = 1 for x = 2,565,007,112,872,132,129,669,406,439,503,954,211,359,492,684,749,762,
                             901,360,167,370,740,763,715,001,557,789,090,674,216,330,243,703,833,
                             040,774,221,628,256,858,633,287,876,949,448,689,668,281,446,637,464,
                             359,482,677,366,420,261,407,112,316,649,010,675,881,349,744,201
                  and y = 27,126,610,172,119,035,540,864,542,981,075,550,089,190,381,938,849,116,
                             323,732,855,930,990,771,728,447,597,698,969,628,164,719,475,714,805,
                             646,913,222,890,277,024,408,337,458,564,351,161,990,641,948,210,581,
                             361,708,373,955,113,191,451,102,494,265,278,824,127,994,180
</pre>

=={{header|Prolog}}==
pell(A, X, Y) finds all solutions X, Y s.t. X^2 - A*Y^2 = 1. Therefore the once() predicate can be used to only select the first one.
<syntaxhighlight lang="prolog">
% Find the square root as a continued fraction

cf_sqrt(N, Sz, [A0, Frac]) :-
    A0 is floor(sqrt(N)),
    (A0*A0 =:= N ->
        Sz = 0, Frac = []
    ;
        cf_sqrt(N, A0, A0, 0, 1, 0, [], Sz, Frac)).

cf_sqrt(N, A, A0, M0, D0, Sz0, L, Sz, R) :-
    M1 is D0*A0 - M0,
    D1 is (N - M1*M1) div D0,
    A1 is (A + M1) div D1,
    (A1 =:= 2*A ->
        succ(Sz0, Sz), revtl([A1|L], R, R)
    ;
        succ(Sz0, Sz1), cf_sqrt(N, A, A1, M1, D1, Sz1, [A1|L], Sz, R)).

revtl([], Z, Z).
revtl([A|As], Bs, Z) :- revtl(As, [A|Bs], Z).


% evaluate an infinite continued fraction as a lazy list of convergents.
% 
convergents([A0, As], Lz) :-
    lazy_list(next_convergent, eval_state(1, 0, A0, 1, As), Lz).

next_convergent(eval_state(P0, Q0, P1, Q1, [Term|Ts]), eval_state(P1, Q1, P2, Q2, Ts), R) :-
    P2 is Term*P1 + P0,
    Q2 is Term*Q1 + Q0,
    R is P1 rdiv Q1.


% solve Pell's equation
%
pell(N, X, Y) :-
    cf_sqrt(N, _, D), convergents(D, Rs),
    once((member(R, Rs), ratio(R, P, Q), P*P - N*Q*Q =:= 1)),
    pell_seq(N, P, Q, X, Y).

ratio(N, N, 1) :- integer(N).
ratio(P rdiv Q, P, Q).

pell_seq(_, X, Y, X, Y).
pell_seq(N, X0, Y0, X2, Y2) :-
    pell_seq(N, X0, Y0, X1, Y1),
    X2 is X0*X1 + N*Y0*Y1,
    Y2 is X0*Y1 + Y0*X1.
</syntaxhighlight>
{{Out}}
<pre>
% show how we can keep generating solutions for x^2 - 3y^2 = 1
?- pell(3,X,Y).
X = 2,
Y = 1 ;
X = 7,
Y = 4 ;
X = 26,
Y = 15 ;
X = 97,
Y = 56 ;
X = 362,
Y = 209 ;
X = 1351,
Y = 780 ;
X = 5042,
Y = 2911 .

% solve the task
?- forall((member(A, [61, 109, 181, 277]), once(pell(A, X, Y))), (write(X**2-A*Y**2=1), nl)).
1766319049**2-61*226153980**2=1
158070671986249**2-109*15140424455100**2=1
2469645423824185801**2-181*183567298683461940**2=1
159150073798980475849**2-277*9562401173878027020**2=1
true.
</pre>
=={{header|Python}}==
{{trans|D}}
<syntaxhighlight lang="python">import math

def solvePell(n):
    x = int(math.sqrt(n))
    y, z, r = x, 1, x << 1
    e1, e2 = 1, 0
    f1, f2 = 0, 1
    while True:
        y = r * z - y
        z = (n - y * y) // z
        r = (x + y) // z

        e1, e2 = e2, e1 + e2 * r
        f1, f2 = f2, f1 + f2 * r

        a, b = f2 * x + e2, f2
        if a * a - n * b * b == 1:
            return a, b

for n in [61, 109, 181, 277]:
    x, y = solvePell(n)
    print("x^2 - %3d * y^2 = 1 for x = %27d and y = %25d" % (n, x, y))</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =                  1766319049 and y =                 226153980
x^2 - 109 * y^2 = 1 for x =             158070671986249 and y =            15140424455100
x^2 - 181 * y^2 = 1 for x =         2469645423824185801 and y =        183567298683461940
x^2 - 277 * y^2 = 1 for x =       159150073798980475849 and y =       9562401173878027020</pre>

=={{header|Raku}}==
(formerly Perl 6)
{{works with|Rakudo|2018.12}}
{{trans|Perl}}

<syntaxhighlight lang="raku" line>use Lingua::EN::Numbers;

sub pell (Int $n) {

    my $y = my $x = Int(sqrt $n);
    my $z = 1;
    my $r = 2 * $x;

    my ($e1, $e2) = (1, 0);
    my ($f1, $f2) = (0, 1);

    loop {
        $y = $r * $z - $y;
        $z = Int(($n - $y²) / $z);
        $r = Int(($x + $y) / $z);

        ($e1, $e2) = ($e2, $r * $e2 + $e1);
        ($f1, $f2) = ($f2, $r * $f2 + $f1);

        my $A = $e2 + $x * $f2;
        my $B = $f2;

        if ($A² - $n * $B² == 1) {
            return ($A, $B);
        }
    }
}

for 61, 109, 181, 277, 8941 -> $n {
    next if $n.sqrt.narrow ~~ Int;
    my ($x, $y) = pell($n);
    printf "x² - %sy² = 1 for:\n\tx = %s\n\ty = %s\n\n", $n, |($x, $y)».&comma;
}</syntaxhighlight>
{{out}}
<pre>x² - 61y² = 1 for:
	x = 1,766,319,049
	y = 226,153,980

x² - 109y² = 1 for:
	x = 158,070,671,986,249
	y = 15,140,424,455,100

x² - 181y² = 1 for:
	x = 2,469,645,423,824,185,801
	y = 183,567,298,683,461,940

x² - 277y² = 1 for:
	x = 159,150,073,798,980,475,849
	y = 9,562,401,173,878,027,020

x² - 8941y² = 1 for:
	x = 2,565,007,112,872,132,129,669,406,439,503,954,211,359,492,684,749,762,901,360,167,370,740,763,715,001,557,789,090,674,216,330,243,703,833,040,774,221,628,256,858,633,287,876,949,448,689,668,281,446,637,464,359,482,677,366,420,261,407,112,316,649,010,675,881,349,744,201
	y = 27,126,610,172,119,035,540,864,542,981,075,550,089,190,381,938,849,116,323,732,855,930,990,771,728,447,597,698,969,628,164,719,475,714,805,646,913,222,890,277,024,408,337,458,564,351,161,990,641,948,210,581,361,708,373,955,113,191,451,102,494,265,278,824,127,994,180</pre>

=={{header|REXX}}==
A little extra code was added to align and commatize the gihugeic numbers for readability.
<syntaxhighlight lang="rexx">/*REXX program to solve Pell's equation for the smallest solution of positive integers. */
numeric digits 2200                              /*ensure enough decimal digs for answer*/
parse arg $                                      /*obtain optional arguments from the CL*/
if $=='' | $==","  then $= 61 109 181 277        /*Not specified?  Then use the defaults*/
d= 28                                            /*used for aligning the output numbers.*/
       do j=1  for words($);    #= word($, j)    /*process all the numbers in the list. */
       parse value   pells(#)   with   x  y      /*extract the two values of  X  and  Y.*/
       cx= comma(x);       Lcx= length(cx);           cy=  comma(y);       Lcy= length(cy)
       say 'x^2 -'right(#, max(4, length(#)))    "* y^2 == 1" ,
                    ' when x='right(cx, max(d, Lcx))     "  and y="right(cy, max(d, Lcy))
       end   /*j*/
exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
comma: parse arg ?;  do jc=length(?)-3  to 1  by -3; ?= insert(',', ?, jc); end;  return ?
floor: procedure; parse arg x;  _= x % 1;          return  _   -    (x < 0)   *   (x \= _)
/*──────────────────────────────────────────────────────────────────────────────────────*/
iSqrt: procedure; parse arg x;  r= 0;     q= 1;           do  while q<=x;  q= q * 4;   end
         do  while q>1; q= q%4; _= x-r-q; r= r%2; if _>=0  then do; x= _; r= r+q; end; end
       return r                                  /*R:  is the integer square root of X. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
pells: procedure; parse arg n; x= iSqrt(n);  y=x /*obtain arg;  obtain integer sqrt of N*/
       parse value  1 0   with   e1 e2  1  f2 f1 /*assign values for: E1, E2, and F2, F1*/
       z= 1;        r= x + x
                                         do  until ( (e2 + x*f2)**2  -  n*f2*f2)  ==  1
                                         y= r*z  -  y;     z= floor( (n - y*y) / z)
                                                           r= floor( (x + y  ) / z)
                                         parse value  e2   r*e2  +  e1     with     e1  e2
                                         parse value  f2   r*f2  +  f1     with     f1  f2
                                         end   /*until*/
       return e2  +  x * f2     f2</syntaxhighlight>
{{out|output|text=&nbsp; when using the default inputs:}}
<pre>
x^2 -  61 * y^2 == 1  when x=               1,766,319,049  and y=                 226,153,980
x^2 - 109 * y^2 == 1  when x=         158,070,671,986,249  and y=          15,140,424,455,100
x^2 - 181 * y^2 == 1  when x=   2,469,645,423,824,185,801  and y=     183,567,298,683,461,940
x^2 - 277 * y^2 == 1  when x= 159,150,073,798,980,475,849  and y=   9,562,401,173,878,027,020
</pre>

=={{header|Ruby}}==
{{trans|Sidef}}
<syntaxhighlight lang="ruby">def solve_pell(n)
  x = Integer.sqrt(n)
  y = x
  z = 1
  r = 2*x
  e1, e2 = 1, 0
  f1, f2 = 0, 1

  loop do
    y = r*z - y
    z = (n - y*y) / z
    r = (x + y) / z
    e1, e2 = e2, r*e2 + e1
    f1, f2 = f2, r*f2 + f1
    a,  b  = e2 + x*f2, f2
    break a, b if a*a - n*b*b == 1
  end
end

[61, 109, 181, 277].each {|n| puts "x*x - %3s*y*y = 1 for x = %-21s and y = %s" % [n, *solve_pell(n)]}
</syntaxhighlight>
{{Out}}
<pre>
x*x -  61*y*y = 1 for x = 1766319049            and y = 226153980
x*x - 109*y*y = 1 for x = 158070671986249       and y = 15140424455100
x*x - 181*y*y = 1 for x = 2469645423824185801   and y = 183567298683461940
x*x - 277*y*y = 1 for x = 159150073798980475849 and y = 9562401173878027020

</pre>
=={{header|Rust}}==
<syntaxhighlight lang="rust">
use num_bigint::{ToBigInt, BigInt};
use num_traits::{Zero, One};
//use std::mem::replace in the loop if you want this to be more efficient

fn main() {
    test(61u64);
    test(109u64);
    test(181u64);
    test(277u64);
}

struct Pair {
    v1: BigInt,
    v2: BigInt,
}

impl Pair {
    pub fn make_pair(a: &BigInt, b: &BigInt) -> Pair {
        Pair {
            v1: a.clone(),
            v2: b.clone(),
        }
    }

}

fn solve_pell(n: u64) -> Pair{
    let x: BigInt = ((n as f64).sqrt()).to_bigint().unwrap();
    if x.clone() * x.clone() == n.to_bigint().unwrap() {
        Pair::make_pair(&One::one(), &Zero::zero())
    } else {
        let mut y: BigInt = x.clone();
        let mut z: BigInt = One::one();
        let mut r: BigInt = ( &z + &z) * x.clone();
        let mut e: Pair = Pair::make_pair(&One::one(), &Zero::zero());
        let mut f: Pair = Pair::make_pair(&Zero::zero() ,&One::one());
        let mut a: BigInt = Zero::zero();
        let mut b: BigInt = Zero::zero();
        while &a * &a - n * &b * &b != One::one() {
            //println!("{}  {}  {}", y, z, r);
            y = &r * &z - &y;
            z = (n - &y * &y) / &z;
            r = (&x + &y) / &z;

            e = Pair::make_pair(&e.v2, &(&r * &e.v2 + &e.v1));
            f = Pair::make_pair(&f.v2, &(&r * &f.v2 + &f.v1));
            a = &e.v2 + &x * &f.v2;
            b = f.v2.clone();
        }
        let pa = &a;
        let pb = &b;
        Pair::make_pair(&pa.clone(), &pb.clone())
    }
}

fn test(n: u64) {
    let r: Pair = solve_pell(n);
    println!("x^2 - {} * y^2 = 1 for x = {} and y = {}", n, r.v1, r.v2);
}
</syntaxhighlight>
{{out}}
<pre>
x^2 - 61 * y^2 = 1 for x = 1766319049 and y = 226153980
x^2 - 109 * y^2 = 1 for x = 158070671986249 and y = 15140424455100
x^2 - 181 * y^2 = 1 for x = 2469645423824185801 and y = 183567298683461940
x^2 - 277 * y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Scala}}==
<syntaxhighlight lang="scala">def pellFermat(n: Int): (BigInt,BigInt) = {
  import scala.math.{sqrt, floor}

  val x = BigInt(floor(sqrt(n)).toInt)

  var i = 0

  // Use the Continued Fractions method
  def converge(y:BigInt, z:BigInt, r:BigInt, e1:BigInt, e2:BigInt, f1:BigInt, f2:BigInt ) : (BigInt,BigInt) = {

    val a = f2 * x + e2
    val b = f2

    if (a * a - n * b * b == 1) {
      return (a, b)
    }

    val yh = r * z - y
    val zh = (n - yh * yh) / z
    val rh = (x + yh) / zh

    converge(yh,zh,rh,e2,e1 + e2 * rh,f2,f1 + f2 * rh)
  }

  converge(x,BigInt("1"),x << 1,BigInt("1"),BigInt("0"),BigInt("0"),BigInt("1"))
}

val nums = List(61,109,181,277)
val solutions = nums.map{pellFermat(_)}

{
  println("For Pell's Equation, x\u00b2 - ny\u00b2 = 1\n")
  (nums zip solutions).foreach{ case (n, (x,y)) => println(s"n = $n, x = $x, y = $y")}
}</syntaxhighlight>
{{out}}
<pre>For Pell's Equation, x² - ny² = 1

n = 61, x = 1766319049, y = 226153980
n = 109, x = 158070671986249, y = 15140424455100
n = 181, x = 2469645423824185801, y = 183567298683461940
n = 277, x = 159150073798980475849, y = 9562401173878027020</pre>

=={{header|Sidef}}==
<syntaxhighlight lang="ruby">func solve_pell(n) {

    var x = n.isqrt
    var y = x
    var z = 1
    var r = 2*x

    var (e1, e2) = (1, 0)
    var (f1, f2) = (0, 1)

    loop {

        y = (r*z - y)
        z = floor((n - y*y) / z)
        r = floor((x + y) / z)

        (e1, e2) = (e2, r*e2 + e1)
        (f1, f2) = (f2, r*f2 + f1)

        var A = (e2 + x*f2)
        var B = f2

        if (A**2 - n*B**2 == 1) {
            return (A, B)
        }
    }
}

for n in [61, 109, 181, 277] {
    var (x, y) = solve_pell(n)
    printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", n, x, y)
}</syntaxhighlight>
{{out}}
<pre>
x^2 -  61*y^2 = 1 for x = 1766319049            and y = 226153980
x^2 - 109*y^2 = 1 for x = 158070671986249       and y = 15140424455100
x^2 - 181*y^2 = 1 for x = 2469645423824185801   and y = 183567298683461940
x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|Swift}}==

{{trans|Kotlin}}
{{libheader|AttaSwift's BigInt}}

<syntaxhighlight lang="swift">func solvePell<T: BinaryInteger>(n: T, _ a: inout T, _ b: inout T) {
  func swap(_ a: inout T, _ b: inout T, mul by: T) {
    (a, b) = (b, b * by + a)
  }

  let x = T(Double(n).squareRoot())
  var y = x
  var z = T(1)
  var r = x << 1
  var e1 = T(1)
  var e2 = T(0)
  var f1 = T(0)
  var f2 = T(1)

  while true {
    y = r * z - y
    z = (n - y * y) / z
    r = (x + y) / z

    swap(&e1, &e2, mul: r)
    swap(&f1, &f2, mul: r)

    (a, b) = (f2, e2)

    swap(&b, &a, mul: x)

    if a * a - n * b * b == 1 {
      return
    }
  }
}

var x = BigInt(0)
var y = BigInt(0)

for n in [61, 109, 181, 277] {
  solvePell(n: BigInt(n), &x, &y)

  print("x\u{00b2} - \(n)y\u{00b2} = 1 for x = \(x) and y = \(y)")
}</syntaxhighlight>

{{out}}

<pre>x² - 61y² = 1 for x = 1766319049 and y = 226153980
x² - 109y² = 1 for x = 158070671986249 and y = 15140424455100
x² - 181y² = 1 for x = 2469645423824185801 and y = 183567298683461940
x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020</pre>

=={{header|Visual Basic .NET}}==
{{trans|Sidef}}
<syntaxhighlight lang="vbnet">Imports System.Numerics

Module Module1
    Sub Fun(ByRef a As BigInteger, ByRef b As BigInteger, c As Integer)
        Dim t As BigInteger = a : a = b : b = b * c + t
    End Sub

    Sub SolvePell(n As Integer, ByRef a As BigInteger, ByRef b As BigInteger)
        Dim x As Integer = Math.Sqrt(n), y As Integer = x, z As Integer = 1, r As Integer = x << 1,
            e1 As BigInteger = 1, e2 As BigInteger = 0, f1 As BigInteger = 0, f2 As BigInteger = 1
        While True
            y = r * z - y : z = (n - y * y) / z : r = (x + y) / z
            Fun(e1, e2, r) : Fun(f1, f2, r) : a = f2 : b = e2 : Fun(b, a, x)
            If a * a - n * b * b = 1 Then Exit Sub
        End While
    End Sub

    Sub Main()
        Dim x As BigInteger, y As BigInteger
        For Each n As Integer In {61, 109, 181, 277}
            SolvePell(n, x, y)
            Console.WriteLine("x^2 - {0,3} * y^2 = 1 for x = {1,27:n0} and y = {2,25:n0}", n, x, y)
        Next
    End Sub
End Module</syntaxhighlight>
{{out}}
<pre>x^2 -  61 * y^2 = 1 for x =               1,766,319,049 and y =               226,153,980
x^2 - 109 * y^2 = 1 for x =         158,070,671,986,249 and y =        15,140,424,455,100
x^2 - 181 * y^2 = 1 for x =   2,469,645,423,824,185,801 and y =   183,567,298,683,461,940
x^2 - 277 * y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020</pre>

=={{header|Wren}}==
{{trans|Sidef}}
{{libheader|Wren-big}}
{{libheader|Wren-fmt}}
<syntaxhighlight lang="wren">import "./big" for BigInt
import "./fmt" for Fmt

var solvePell = Fn.new { |n|
    n = BigInt.new(n)
    var x = n.isqrt
    var y = x.copy()
    var z = BigInt.one
    var r = x * 2
    var e1 = BigInt.one
    var e2 = BigInt.zero
    var f1 = BigInt.zero
    var f2 = BigInt.one
    while (true) {
        y = r*z - y
        z = (n - y*y) / z
        r = (x + y) / z
        var t = e1.copy()
        e1 = e2.copy()
        e2 = r*e2 + t
        t = f1.copy()
        f1 = f2.copy()
        f2 = r*f2 + t
        var a = e2 + x*f2
        var b = f2.copy()
        if (a*a - n*b*b == BigInt.one) return [a, b]
    }
}

for (n in [61, 109, 181, 277]) {
    var res = solvePell.call(n)
    Fmt.print("x² - $3dy² = 1 for x = $-21i and y = $i", n, res[0], res[1])
}</syntaxhighlight>

{{out}}
<pre>
x² -  61y² = 1 for x = 1766319049            and y = 226153980
x² - 109y² = 1 for x = 158070671986249       and y = 15140424455100
x² - 181y² = 1 for x = 2469645423824185801   and y = 183567298683461940
x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>

=={{header|zkl}}==
{{libheader|GMP}} GNU Multiple Precision Arithmetic Library
{{trans|Raku}}
<syntaxhighlight lang="zkl">var [const] BI=Import("zklBigNum");  // libGMP

fcn solve_pell(n){
   x,y,z,r := BI(n).root(2),  x.copy(),  BI(1),  x*2;
   e1,e2, f1,f2 := BI(1), BI(0),  BI(0), BI(1);
   reg t;	// a,b = c,d is a=c; b=d
   do(30_000){  // throttle this in case of screw up
      y,z,r = (r*z - y),  (n - y*y)/z,  (x + y)/z;
 
      t,e2,e1 = e2,  r*e2 + e1,  t;
      t,f2,f1 = f2,  r*f2 + f1,  t;

      A,B := e2 + x*f2, f2;

      if (A*A - B*B*n == 1) return(A,B);
   }
}</syntaxhighlight>
<syntaxhighlight lang="zkl">foreach n in (T(61, 109, 181, 277)){
   x,y:=solve_pell(n);
   println("x^2 - %3d*y^2 = 1 for x = %-21d and y = %d".fmt(n,x,y));
}</syntaxhighlight>

{{out}}
<pre>
x^2 -  61*y^2 = 1 for x = 1766319049            and y = 226153980
x^2 - 109*y^2 = 1 for x = 158070671986249       and y = 15140424455100
x^2 - 181*y^2 = 1 for x = 2469645423824185801   and y = 183567298683461940
x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
</pre>