Special neighbor primes

Special neighbor primes is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Task

Let   (p₁,  p₂)   are neighbor primes. Find and show here in base ten if p₁+ p₂ -1 is prime,  where   p₁,   p₂  <  100.

F#

This task uses Extensible Prime Generator (F#) <lang fsharp> // Special neighbor primes. Nigel Galloway: August 6th., 2021 pCache|>Seq.pairwise|>Seq.takeWhile(snd>>(>)100)|>Seq.filter(fun(n,g)->isPrime(n+g-1))|>Seq.iter(printfn "%A") </lang>

Output:

(3, 5)
(5, 7)
(7, 11)
(11, 13)
(13, 17)
(19, 23)
(29, 31)
(31, 37)
(41, 43)
(43, 47)
(61, 67)
(67, 71)
(73, 79)

Factor

Works with: Factor version 0.99 2021-06-02

<lang factor>USING: kernel lists lists.lazy math math.primes math.primes.lists prettyprint sequences ;

lprimes dup cdr lzip [ sum 1 - prime? ] lfilter [ second 100 < ] lwhile [ . ] leach</lang>

Output:

{ 3 5 }
{ 5 7 }
{ 7 11 }
{ 11 13 }
{ 13 17 }
{ 19 23 }
{ 29 31 }
{ 31 37 }
{ 41 43 }
{ 43 47 }
{ 61 67 }
{ 67 71 }
{ 73 79 }

Go

Translation of: Wren

Library: Go-rcu

<lang go>package main

import (

   "fmt"
   "rcu"

)

const MAX = 1e7 - 1

var primes = rcu.Primes(MAX)

func specialNP(limit int, showAll bool) {

   if showAll {
       fmt.Println("Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:")
   }
   count := 0
   for i := 1; i < len(primes); i++ {
       p2 := primes[i]
       if p2 >= limit {
           break
       }
       p1 := primes[i-1]
       p3 := p1 + p2 - 1
       if rcu.IsPrime(p3) {
           if showAll {
               fmt.Printf("(%2d, %2d) => %3d\n", p1, p2, p3)
           }
           count++
       }
   }
   ccount := rcu.Commatize(count)
   climit := rcu.Commatize(limit)
   fmt.Printf("\nFound %s special neighbor primes under %s.\n", ccount, climit)

}

func main() {

   specialNP(100, true)
   var pow = 1000
   for i := 3; i < 8; i++ {
       specialNP(pow, false)
       pow *= 10
   }

}</lang>

Output:

Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:
( 3,  5) =>   7
( 5,  7) =>  11
( 7, 11) =>  17
(11, 13) =>  23
(13, 17) =>  29
(19, 23) =>  41
(29, 31) =>  59
(31, 37) =>  67
(41, 43) =>  83
(43, 47) =>  89
(61, 67) => 127
(67, 71) => 137
(73, 79) => 151

Found 13 special neighbor primes under 100.

Found 71 special neighbor primes under 1,000.

Found 367 special neighbor primes under 10,000.

Found 2,165 special neighbor primes under 100,000.

Found 14,526 special neighbor primes under 1,000,000.

Found 103,611 special neighbor primes under 10,000,000.

Julia

<lang julia>using Primes

function specialneighbors(N)

   neighbors, p1 = Pair{Int}[], 2
   while (p2 = nextprime(p1 + 2)) < N
       isprime(p2 + p1 - 1) && push!(neighbors, p1 => p2)
       p1 = p2
   end
   return neighbors

end

println("Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:") println("p1 p2 p1 + p2 - 1\n--------------------------") for (p1, p2) in specialneighbors(100)

   println(lpad(p1, 2), "   ", rpad(p2, 7), p1 + p2 - 1)

end

</lang>

Output:

Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:
p1   p2   p1 + p2 - 1
--------------------------
 5   7      11
 7   11     17
11   13     23
13   17     29
19   23     41
29   31     59
31   37     67
41   43     83
43   47     89
61   67     127
67   71     137
73   79     151

Nim

<lang Nim>import strutils, sugar

const Max = 100 - 1

func isPrime(n: Positive): bool =

 if n == 1: return false
 if n mod 2 == 0: return n == 2
 for d in countup(3, n, 2):
   if d * d > n: break
   if n mod d == 0: return false
 result = true

const Primes = collect(newSeq):

                for n in 2..Max:
                  if n.isPrime: n

let list = collect(newSeq):

            for i in 0..<Primes.high:
              let p1 = Primes[i]
              let p2 = Primes[i + 1]
              if (p1 + p2 - 1).isPrime: (p1, p2)

echo "Found $1 special neighbor primes less than $2:".format(list.len, Max + 1) echo list.join(", ")</lang>

Output:

Found 13 special neighbor primes less than 100:
(3, 5), (5, 7), (7, 11), (11, 13), (13, 17), (19, 23), (29, 31), (31, 37), (41, 43), (43, 47), (61, 67), (67, 71), (73, 79)

REXX

<lang rexx>/*REXX program finds neighbor primes: P1, P2, P1+P2-1 are primes, and P1 and P2 < 100*/ parse arg hi cols . /*obtain optional argument from the CL.*/ if hi== | hi=="," then hi= 100 /*Not specified? Then use the default.*/ if cols== | cols=="," then cols= 5 /* " " " " " " */ call genP hi /*build semaphore array for low primes.*/

    do p=1  while @.p<hi
    end  /*p*/;           lim= p-1;   q= p+1    /*set LIM to prime for P; calc. 2nd HI.*/

1. m= # - 1

call genP @.# + @.#m - 1 /*build semaphore array for high primes*/ w= 20 /*width of a number in any column. */ title= ' special neighbor primes: P1, P2, P1+P2-1 are primes, and P1 and P2 < ' ,

                                                                     commas(hi)

if cols>0 then say ' index │'center(title, 1 + cols*(w+1) ) if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') found= 0; idx= 1 /*initialize # neighbor primes & index.*/ $= /*a list of neighbor primes (so far).*/

    do j=1  to  lim;      jp= j+1;   q= @.jp    /*look for neighbor primes within range*/
    y= @.j + q  -  1;     if \!.y  then iterate /*is X also a prime?  No, then skip it.*/
    found= found + 1                            /*bump the number of  neighbor primes. */
    if cols==0            then iterate          /*Build the list  (to be shown later)? */
    $= $  right( @.j','q"──►"y, w)              /*add neighbor prime ──► the  $  list. */
    if found//cols\==0  then iterate            /*have we populated a line of output?  */
    say center(idx, 7)'│'  substr($, 2);   $=   /*display what we have so far  (cols). */
    idx= idx + cols                             /*bump the  index  count for the output*/
    end   /*j*/

if $\== then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/ if cols>0 then say '───────┴'center("" , 1 + cols*(w+1), '─') say say 'Found ' commas(found) title exit 0 /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ commas: parse arg ?; do jc=length(?)-3 to 1 by -3; ?=insert(',', ?, jc); end; return ? /*──────────────────────────────────────────────────────────────────────────────────────*/ genP: !.= 0; parse arg limit /*placeholders for primes (semaphores).*/

     @.1=2;  @.2=3;  @.3=5;  @.4=7;  @.5=11     /*define some low primes.              */
     !.2=1;  !.3=1;  !.5=1;  !.7=1;  !.11=1     /*   "     "   "    "     flags.       */
                       #=5;     s.#= @.# **2    /*number of primes so far;     prime². */
                                                /* [↓]  generate more  primes  ≤  high.*/
       do j=@.#+2  by 2  to limit               /*find odd primes from here on.        */
       parse var j  -1 _; if     _==5  then iterate  /*J divisible by 5?  (right dig)*/
                            if j// 3==0  then iterate  /*"     "      " 3?             */
                            if j// 7==0  then iterate  /*"     "      " 7?             */
                                                /* [↑]  the above  3  lines saves time.*/
              do k=5  while s.k<=j              /* [↓]  divide by the known odd primes.*/
              if j // @.k == 0  then iterate j  /*Is  J ÷ X?  Then not prime.     ___  */
              end   /*k*/                       /* [↑]  only process numbers  ≤  √ J   */
       #= #+1;    @.#= j;    s.#= j*j;   !.j= 1 /*bump # of Ps; assign next P;  P²; P# */
       end          /*j*/;   return</lang>

output   when using the default inputs:

 index │               special neighbor primes:  P1, P2, P1+P2-1  are primes,  and P1 and P2 <  100
───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │              3,5──►7             5,7──►11            7,11──►17           11,13──►23           13,17──►29
   6   │           19,23──►41           29,31──►59           31,37──►67           41,43──►83           43,47──►89
  11   │          61,67──►127          67,71──►137          73,79──►151
───────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────

Found  13  special neighbor primes:  P1, P2, P1+P2-1  are primes,  and P1 and P2 <  100

Ring

<lang ring> load "stdlib.ring"

see "working..." + nl see "Special neighbor primes are:" + nl row = 0 oldPrime = 2

for n = 3 to 100

   if isprime(n) and isprime(oldPrime) 
      sum = oldPrime + n - 1
      if isprime(sum)
         row++
         see "" + oldPrime + "," + n + " => " + sum + nl
      ok
      oldPrime = n
   ok

next

see "Found " + row + " special neighbor primes" see "done..." + nl </lang>

Output:

working...
Special neighbor primes are:
3,5 => 7
5,7 => 11
7,11 => 17
11,13 => 23
13,17 => 29
19,23 => 41
29,31 => 59
31,37 => 67
41,43 => 83
43,47 => 89
61,67 => 127
67,71 => 137
73,79 => 151
Found 13 special neighbor primes
done...

Wren

Library: Wren-math

Library: Wren-fmt

I assume that 'neighbor' primes means pairs of successive primes.

Anticipating a likely stretch goal. <lang ecmascript>import "/math" for Int import "/fmt" for Fmt

var max = 1e7 - 1 var primes = Int.primeSieve(max)

var specialNP = Fn.new { |limit, showAll|

   if (showAll) System.print("Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:")
   var count = 0
   var p3
   for (i in 1...primes.where { |p| p < limit }.count) {
       var p2 = primes[i]
       var p1 = primes[i-1]
       if (Int.isPrime(p3 = p1 + p2 - 1)) {
           if (showAll) Fmt.print("($2d, $2d) => $3d", p1, p2, p3)
           count = count + 1
       }
   }
   Fmt.print("\nFound $,d special neighbor primes under $,d.", count, limit)

}

specialNP.call(100, true) for (i in 3..7) {

   specialNP.call(10.pow(i), false)

}</lang>

Output:

Neighbor primes, p1 and p2, where p1 + p2 - 1 is prime:
( 3,  5) =>   7
( 5,  7) =>  11
( 7, 11) =>  17
(11, 13) =>  23
(13, 17) =>  29
(19, 23) =>  41
(29, 31) =>  59
(31, 37) =>  67
(41, 43) =>  83
(43, 47) =>  89
(61, 67) => 127
(67, 71) => 137
(73, 79) => 151

Found 13 special neighbor primes under 100.

Found 71 special neighbor primes under 1,000.

Found 367 special neighbor primes under 10,000.

Found 2,165 special neighbor primes under 100,000.

Found 14,526 special neighbor primes under 1,000,000.

Found 103,611 special neighbor primes under 10,000,000.

XPL0

<lang XPL0>func IsPrime(N); \Return 'true' if N is a prime number int N, I; [if N <= 1 then return false; for I:= 2 to sqrt(N) do

   if rem(N/I) = 0 then return false;

return true; ];

int P, P1, P2; [P:= 2; loop [P1:= P;

       repeat  P:= P+1;
               if P >= 100 then quit;
       until   IsPrime(P);
       P2:= P;
       if IsPrime(P1+P2-1) then
               [IntOut(0, P1);  ChOut(0, ^ );
                IntOut(0, P2);  ChOut(0, ^ );
                IntOut(0, P1+P2-1);  CrLf(0);
               ];
       ];

]</lang>

Output:

3 5 7
5 7 11
7 11 17
11 13 23
13 17 29
19 23 41
29 31 59
31 37 67
41 43 83
43 47 89
61 67 127
67 71 137
73 79 151