Frobenius numbers

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Revision as of 14:24, 3 May 2021 by Simonjsaunders (talk | contribs) (Added C++ solution)
Frobenius numbers 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

Find and display here on this page the Frobenius numbers   <   10,000.


The series is defined by: 

   FrobeniusNumber(n)  =  prime(n) * prime(n+1)   -   prime(n)   -   prime(n+1)

-where:

  prime(1)   =   2
  prime(2)   =   3
  prime(3)   =   5
  prime(4)   =   7     • • •



ALGOL 68

<lang algol68>BEGIN # find some Frobenius Numbers: # 

     #     Frobenius(n) = ( prime(n) * prime(n+1) ) - prime(n) - prime(n+1) #
   # reurns a list of primes up to n #
   PROC prime list = ( INT n )[]INT:
        BEGIN
           # sieve the primes to n #
           INT no = 0, yes = 1;
           [ 1 : n ]INT p;
           p[ 1 ] := no; p[ 2 ] := yes;
           FOR i FROM 3 BY 2 TO n DO p[ i ] := yes OD;
           FOR i FROM 4 BY 2 TO n DO p[ i ] := no  OD;
           FOR i FROM 3 BY 2 TO ENTIER sqrt( n ) DO
               IF p[ i ] = yes THEN FOR s FROM i * i BY i + i TO n DO p[ s ] := no OD FI
           OD;
           # replace the sieve with a list #
           INT p pos := 0;
           FOR i TO n DO IF p[ i ] = yes THEN p[ p pos +:= 1 ] := i FI OD;
           p[ 1 : p pos ]
        END # prime list # ;
   # show Frobenius numbers up to 10 000 #
   INT max number = 10 000;
   []INT prime    = prime list( max number );
   FOR i TO max number - 1
   WHILE INT frobenius number = ( ( prime[ i ] * prime[ i + 1 ] ) - prime[ i ] ) - prime[ i + 1 ];
             frobenius number < max number
   DO
       print( ( " ", whole( frobenius number, 0 ) ) )
   OD

END</lang>

Output:
 1 7 23 59 119 191 287 395 615 839 1079 1439 1679 1931 2391 3015 3479 3959 4619 5039 5615 6395 7215 8447 9599

AWK

<lang AWK>

  1. syntax: GAWK -f FROBENIUS_NUMBERS.AWK
  2. converted from FreeBASIC

BEGIN { 

   start = 3
   stop = 9999
   pn = 2
   for (i=start; i<=stop; i++) {
     if (is_prime(i)) {
       f = pn * i - pn - i
       if (f > stop) { break }
       printf("%4d%1s",f,++count%10?"":"\n")
       pn = i
     }
   }
   printf("\nFrobenius numbers %d-%d: %d\n",start,stop,count)
   exit(0)

} function is_prime(x, i) { 

   if (x <= 1) {
     return(0)
   }
   for (i=2; i<=int(sqrt(x)); i++) {
     if (x % i == 0) {
       return(0)
     }
   }
   return(1)

} </lang>

Output:
   1    7   23   59  119  191  287  395  615  839
1079 1439 1679 1931 2391 3015 3479 3959 4619 5039
5615 6395 7215 8447 9599
Frobenius numbers 3-9999: 25

C#

Asterisks mark the non-primes among the numbers. <lang csharp>using System.Collections.Generic; using System.Linq; using static System.Console; using static System.Math;

class Program { 

   static bool ispr(int x) { int lim = (int)Sqrt((double)x);
       if (x < 2) return false; if ((x % 3) == 0) return x == 0; bool odd = false;
       for (int d = 5; d <= lim; d += (odd = !odd) ? 2 : 4) {
       if (x % d == 0) return false; } return true; }

   static void Main() {
       int c = 0, d = 0, f, lim = 1000000, l2 = lim / 100; var Frob = PG.Primes((int)Sqrt(lim) + 1).ToArray();
       for (int n = 0, m = 1; m < Frob.Length; n = m++) {
           if ((f = Frob[n] * Frob[m] - Frob[n] - Frob[m]) < l2) d++;
           Write("{0,7:n0}{2} {1}", f , ++c % 10 == 0 ? "\n" : "", ispr(f) ? " " : "*"); }
       Write("\n\nCalculated {0} Frobenius numbers of consecutive primes under {1:n0}, " +
           "of which {2} were under {3:n0}", c, lim, d, l2); } }

class PG { public static IEnumerable<int> Primes(int lim) { 

   var flags = new bool[lim + 1]; int j = 3; yield return 2; 
   for (int d = 8, sq = 9; sq <= lim; j += 2, sq += d += 8)
     if (!flags[j]) { yield return j;
       for (int k = sq, i = j << 1; k <= lim; k += i) flags[k] = true; }
   for (; j <= lim; j += 2) if (!flags[j]) yield return j; } }</lang>
Output:
      1*       7       23       59      119*     191      287*     395*     615*     839  
  1,079*   1,439    1,679*   1,931    2,391*   3,015*   3,479*   3,959*   4,619*   5,039  
  5,615*   6,395*   7,215*   8,447    9,599*  10,199*  10,811*  11,447   12,095*  14,111* 
 16,379*  17,679*  18,767*  20,423*  22,199*  23,399   25,271*  26,891   28,551*  30,615* 
 32,039*  34,199*  36,479   37,631*  38,807*  41,579   46,619   50,171*  51,527*  52,895* 
 55,215*  57,119   59,999   63,999*  67,071*  70,215*  72,359*  74,519*  77,279   78,959* 
 82,343*  89,351*  94,859*  96,719*  98,591* 104,279* 110,879  116,255* 120,407* 122,495* 
126,015* 131,027* 136,151* 140,615* 144,395* 148,215* 153,647* 158,399* 163,199  170,543* 
175,559* 180,599* 185,759* 189,215* 193,595* 198,015* 204,287* 209,759* 212,519* 215,291* 
222,747* 232,307  238,139* 244,019* 249,995* 255,015* 264,159* 271,439* 281,879* 294,839* 
303,575* 312,471* 319,215* 323,759  328,319* 337,535* 346,911* 354,015* 358,799* 363,599* 
370,871  376,991* 380,687* 389,339* 403,199* 410,879* 414,731  421,191* 429,015* 434,279* 
443,519* 454,271* 461,031* 470,579  482,999* 495,599* 508,343* 521,267  531,431* 540,215* 
547,595* 556,499* 566,999  574,559* 583,679* 592,895* 606,791  625,655* 643,167* 654,479* 
664,199  674,039* 678,971  683,927* 693,863* 713,975* 729,311* 734,447* 739,595* 755,111* 
770,879* 776,159  781,451* 802,715* 824,459  835,379  851,903* 868,607* 879,839  889,239* 
900,591* 919,631  937,019* 946,719* 958,431* 972,179* 986,039* 

Calculated 167 Frobenius numbers of consecutive primes under 1,000,000, of which 25 were under 10,000

C++

Library: Primesieve

<lang cpp>#include <cstdint>

  1. include <iomanip>
  2. include <iostream>
  3. include <primesieve.hpp>

bool is_prime(uint64_t n) { 

   if (n < 2)
       return false;
   if (n % 2 == 0)
       return n == 2;
   if (n % 3 == 0)
       return n == 3;
   for (uint64_t p = 5; p * p <= n; p += 4) {
       if (n % p == 0)
           return false;
       p += 2;
       if (n % p == 0)
           return false;
   }
   return true;

}

int main() { 

   const uint64_t limit = 1000000;
   std::cout << "Frobenius numbers less than " << limit
             << " (asterisk marks primes):\n";
   primesieve::iterator it;
   uint64_t prime1 = it.next_prime();
   for (int count = 1;; ++count) {
       uint64_t prime2 = it.next_prime();
       uint64_t frobenius = prime1 * prime2 - prime1 - prime2;
       if (frobenius >= limit)
           break;
       std::cout << std::setw(6) << frobenius
                 << (is_prime(frobenius) ? '*' : ' ')
                 << (count % 10 == 0 ? '\n' : ' ');
       prime1 = prime2;
   }
   std::cout << '\n';

}</lang>

Output:
Frobenius numbers less than 1000000 (asterisk marks primes):
     1       7*     23*     59*    119     191*    287     395     615     839*
  1079    1439*   1679    1931*   2391    3015    3479    3959    4619    5039*
  5615    6395    7215    8447*   9599   10199   10811   11447*  12095   14111 
 16379   17679   18767   20423   22199   23399*  25271   26891*  28551   30615 
 32039   34199   36479*  37631   38807   41579*  46619*  50171   51527   52895 
 55215   57119*  59999*  63999   67071   70215   72359   74519   77279*  78959 
 82343   89351   94859   96719   98591  104279  110879* 116255  120407  122495 
126015  131027  136151  140615  144395  148215  153647  158399  163199* 170543 
175559  180599  185759  189215  193595  198015  204287  209759  212519  215291 
222747  232307* 238139  244019  249995  255015  264159  271439  281879  294839 
303575  312471  319215  323759* 328319  337535  346911  354015  358799  363599 
370871* 376991  380687  389339  403199  410879  414731* 421191  429015  434279 
443519  454271  461031  470579* 482999  495599  508343  521267* 531431  540215 
547595  556499  566999* 574559  583679  592895  606791* 625655  643167  654479 
664199* 674039  678971* 683927  693863  713975  729311  734447  739595  755111 
770879  776159* 781451  802715  824459* 835379* 851903  868607  879839* 889239 
900591  919631* 937019  946719  958431  972179  986039

Factor

Works with: Factor version 0.99 2021-02-05

<lang factor>USING: io kernel math math.primes prettyprint ;

"Frobenius numbers < 10,000:" print 2 3 [ 

   [ nip dup next-prime ] [ * ] [ [ - ] dip - ] 2tri
   dup 10,000 <

] [ . ] while 3drop</lang>

Output:
Frobenius numbers < 10,000:
1
7
23
59
119
191
287
395
615
839
1079
1439
1679
1931
2391
3015
3479
3959
4619
5039
5615
6395
7215
8447
9599

Fermat

<lang fermat>Function Frobenius(n)=Prime(n)*Prime(n+1)-Prime(n)-Prime(n+1). for n = 1 to 25 do !!Frobenius(n) od</lang>

Output:
1
7
23
59
119
191
287
395
615
839
1079
1439
1679
1931
2391
3015
3479
3959
4619
5039
5615
6395
7215
8447
9599

FreeBASIC

<lang freebasic>#include "isprime.bas"

dim as integer pn=2, n=0, f for i as integer = 3 to 9999 step 2 

   if isprime(i) then
       n += 1
       f = pn*i - pn - i
       if f > 10000 then end
       print n, f
       pn = i
   end if

next i</lang>

Output:
 1             1
 2             7
 3             23
 4             59
 5             119
 6             191
 7             287
 8             395
 9             615
 10            839
 11            1079
 12            1439
 13            1679
 14            1931
 15            2391
 16            3015
 17            3479
 18            3959
 19            4619
 20            5039
 21            5615
 22            6395
 23            7215
 24            8447
 25            9599

J

<lang J>frob =: (p:*p:@>:)-p:+p:@>: echo frob i. 25</lang>

Output:
1 7 23 59 119 191 287 395 615 839 1079 1439 1679 1931 2391 3015 3479 3959 4619 5039 5615 6395 7215 8447 9599

Java

Uses the PrimeGenerator class from Extensible prime generator#Java. <lang java>public class Frobenius { 

   public static void main(String[] args) {
       final int limit = 1000000;
       System.out.printf("Frobenius numbers less than %d (asterisk marks primes):\n", limit);
       PrimeGenerator primeGen = new PrimeGenerator(1000, 100000);
       int prime1 = primeGen.nextPrime();
       for (int count = 1; ; ++count) {
           int prime2 = primeGen.nextPrime();
           int frobenius = prime1 * prime2 - prime1 - prime2;
           if (frobenius >= limit)
               break;
           System.out.printf("%6d%c%c", frobenius,
                   isPrime(frobenius) ? '*' : ' ',
                   count % 10 == 0 ? '\n' : ' ');
           prime1 = prime2;
       }
       System.out.println();
   }

   private static boolean isPrime(int n) {
       if (n < 2)
           return false;
       if (n % 2 == 0)
           return n == 2;
       if (n % 3 == 0)
           return n == 3;
       for (int p = 5; p * p <= n; p += 4) {
           if (n % p == 0)
               return false;
           p += 2;
           if (n % p == 0)
               return false;
       }
       return true;
   }

}</lang>

Output:
Frobenius numbers less than 1000000 (asterisk marks primes):
     1       7*     23*     59*    119     191*    287     395     615     839*
  1079    1439*   1679    1931*   2391    3015    3479    3959    4619    5039*
  5615    6395    7215    8447*   9599   10199   10811   11447*  12095   14111 
 16379   17679   18767   20423   22199   23399*  25271   26891*  28551   30615 
 32039   34199   36479*  37631   38807   41579*  46619*  50171   51527   52895 
 55215   57119*  59999*  63999   67071   70215   72359   74519   77279*  78959 
 82343   89351   94859   96719   98591  104279  110879* 116255  120407  122495 
126015  131027  136151  140615  144395  148215  153647  158399  163199* 170543 
175559  180599  185759  189215  193595  198015  204287  209759  212519  215291 
222747  232307* 238139  244019  249995  255015  264159  271439  281879  294839 
303575  312471  319215  323759* 328319  337535  346911  354015  358799  363599 
370871* 376991  380687  389339  403199  410879  414731* 421191  429015  434279 
443519  454271  461031  470579* 482999  495599  508343  521267* 531431  540215 
547595  556499  566999* 574559  583679  592895  606791* 625655  643167  654479 
664199* 674039  678971* 683927  693863  713975  729311  734447  739595  755111 
770879  776159* 781451  802715  824459* 835379* 851903  868607  879839* 889239 
900591  919631* 937019  946719  958431  972179  986039

Julia

<lang julia>using Primes

const primeslt10k = primes(10000) frobenius(n) = begin (x, y) = primeslt10k[n:n+1]; x * y - x - y end

function frobeniuslessthan(maxnum) 

   frobpairs = Pair{Int, Bool}[]
   for n in 1:maxnum
       frob = frobenius(n)
       frob > maxnum && break
       push!(frobpairs, Pair(frob, isprime(frob)))
   end
   return frobpairs

end

function testfrobenius() 

   println("Frobenius numbers less than 1,000,000 (an asterisk marks the prime ones).")
   frobpairs = frobeniuslessthan(1_000_000)
   for (i, p) in enumerate(frobpairs)
       print(rpad(string(p[1]) * (p[2] ? "*" : ""), 8), i % 10 == 0 ? "\n" : "")
   end

end

testfrobenius()

</lang>

Output:
Frobenius numbers less than 1,000,000 (an asterisk marks the prime ones).
1       7*      23*     59*     119     191*    287     395     615     839*    
1079    1439*   1679    1931*   2391    3015    3479    3959    4619    5039*   
5615    6395    7215    8447*   9599    10199   10811   11447*  12095   14111   
16379   17679   18767   20423   22199   23399*  25271   26891*  28551   30615   
32039   34199   36479*  37631   38807   41579*  46619*  50171   51527   52895   
55215   57119*  59999*  63999   67071   70215   72359   74519   77279*  78959   
82343   89351   94859   96719   98591   104279  110879* 116255  120407  122495  
126015  131027  136151  140615  144395  148215  153647  158399  163199* 170543  
175559  180599  185759  189215  193595  198015  204287  209759  212519  215291  
222747  232307* 238139  244019  249995  255015  264159  271439  281879  294839
303575  312471  319215  323759* 328319  337535  346911  354015  358799  363599
370871* 376991  380687  389339  403199  410879  414731* 421191  429015  434279
443519  454271  461031  470579* 482999  495599  508343  521267* 531431  540215
547595  556499  566999* 574559  583679  592895  606791* 625655  643167  654479
664199* 674039  678971* 683927  693863  713975  729311  734447  739595  755111
770879  776159* 781451  802715  824459* 835379* 851903  868607  879839* 889239
900591  919631* 937019  946719  958431  972179  986039

Perl

Library: ntheory

<lang perl>use strict; use warnings; use ntheory 'nth_prime';

my(@F,$n); do { ++$n and push @F, nth_prime($n) * nth_prime($n+1) - (nth_prime($n) + nth_prime($n+1)) } until $F[-1] >= 10000; print "$#F matching numbers:\n" . join(' ', @F[0 .. $#F-1]) . "\n";</lang>

Output:
25 matching numbers:
1 7 23 59 119 191 287 395 615 839 1079 1439 1679 1931 2391 3015 3479 3959 4619 5039 5615 6395 7215 8447 9599

Phix

for n=4 to 6 by 2 do
    integer lim = power(10,n), i=1
    sequence frob = {}
    while true do
        integer p = get_prime(i),
                q = get_prime(i+1),
                frobenius = p*q-p-q
        if frobenius > lim then exit end if
        frob &= frobenius
        i += 1
    end while
    frob = apply(true,sprintf,{{"%d"},frob})
    printf(1,"%3d Frobenius numbers under %,9d: %s\n",
             {length(frob),lim,join(shorten(frob,"",5),", ")})
end for
Output:
 25 Frobenius numbers under    10,000: 1, 7, 23, 59, 119, ..., 5615, 6395, 7215, 8447, 9599
167 Frobenius numbers under 1,000,000: 1, 7, 23, 59, 119, ..., 937019, 946719, 958431, 972179, 986039

Raku

<lang perl6>say "{+$_} matching numbers\n{.batch(10)».fmt('%4d').join: "\n"}\n" 

   given (^1000).grep( *.is-prime ).rotor(2 => -1)
   .map( { (.[0] * .[1] - .[0] - .[1]) } ).grep(* < 10000);</lang>
Output:
25 matching numbers
   1    7   23   59  119  191  287  395  615  839
1079 1439 1679 1931 2391 3015 3479 3959 4619 5039
5615 6395 7215 8447 9599

REXX

<lang rexx>/*REXX program finds Frobenius numbers where the numbers are less than some number N. */ parse arg hi cols . /*obtain optional argument from the CL.*/ if hi== | hi=="," then hi= 10000 /* " " " " " " */ if cols== | cols=="," then cols= 10 /* " " " " " " */ call genP /*build array of semaphores for primes.*/ 

                                   @Frob= ' Frobenius numbers that are  < '    commas(hi)

if cols>0 then say ' index │'center(@Frob, 1 + cols*(w+1) ) if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') $=; idx= 1 /*list of Frobenius #s (so far); index.*/ 

    do j=1;  jp= j+1;  y= @.j*@.jp - @.j - @.jp /*calculate a Frobenius number.        */
    if y>= hi       then leave                  /*Is  Y  too high?  Yes, then leave.   */
    if cols==0      then iterate                /*Build the list  (to be shown later)? */
    c= commas(y)                                /*maybe add commas to the number.      */
    $= $ right(c, max(w, length(c) ) )          /*add a Frobenius #──►list, allow big #*/
    if j//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(j-1) @FROB 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: @.1=2; @.2=3; @.3=5; @.4=7; @.5=11; @.6= 13 /*define some low primes. */ 

     w= 10;            #=6;     s.#= @.# **2          /*number of primes so far; prime²*/
                                                /* [↓]  generate more  primes  ≤  high.*/
       do j=@.#+4  by 2  to hi+1                /*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?            */
                            if j//11==0  then iterate  /*"     "      " 11?            */
                                                /* [↑]  the above four lines saves time*/
              do k=6  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           /*bump # Ps;  assign next P;  P squared*/
       end          /*j*/;   return</lang>
output   when using the default inputs:
 index │                                     Frobenius numbers that are  <  10,000
───────┼───────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │          1          7         23         59        119        191        287        395        615        839
  11   │      1,079      1,439      1,679      1,931      2,391      3,015      3,479      3,959      4,619      5,039
  21   │      5,615      6,395      7,215      8,447      9,599
───────┴───────────────────────────────────────────────────────────────────────────────────────────────────────────────

Found  25  Frobenius numbers that are  <  10,000

Ring

This example is incorrect. Please fix the code and remove this message.

Details: 9599 missing

<lang ring>load "stdlib.ring" # for isprime() function ? "working..." + nl + "Frobenius numbers are:"

  1. create table of prime numbers between 3 and 100 inclusive

Frob = [] for n = 3 to 100 

   if isprime(n) Add(Frob,n) ok

next

m = 1 for n = 2 to len(Frob) 

   fr = Frob[n] * Frob[m] - Frob[n] - Frob[m]
   see sf(fr, 4) + " "
   if m % 5 = 0 see nl ok
   m = n

next

? nl + nl + "Found " + m + " Frobenius numbers" + nl + "done..."

  1. a very plain string formatter, intended to even up columnar outputs

def sf x, y 

   s = string(x) l = len(s)
   if l > y y = l ok
   return substr("          ", 11 - y + l) + s</lang>
Output:
working...
Frobenius numbers are:
   7   23   59  119  191 
 287  395  615  839 1079 
1439 1679 1931 2391 3015 
3479 3959 4619 5039 5615 
6395 7215 8447 

Found 24 Frobenius numbers
done...

Rust

<lang rust>// [dependencies] // primal = "0.3"

fn frobenius_numbers() -> impl std::iter::Iterator<Item = (usize, bool)> { 

   let mut primes = primal::Primes::all();
   let mut prime = primes.next().unwrap();
   std::iter::from_fn(move || {
       if let Some(p) = primes.by_ref().next() {
           let fnum = prime * p - prime - p;
           prime = p;
           return Some((fnum, primal::is_prime(fnum as u64)));
       }
       None
   })

}

fn main() { 

   let limit = 1000000;
   let mut count = 0;
   println!(
       "Frobenius numbers less than {} (asterisk marks primes):",
       limit
   );
   for (fnum, is_prime) in frobenius_numbers().take_while(|(x, _)| *x < limit) {
       count += 1;
       let c = if is_prime { '*' } else { ' ' };
       let s = if count % 10 == 0 { '\n' } else { ' ' };
       print!("{:6}{}{}", fnum, c, s);
   }
   println!();

}</lang>

Output:
Frobenius numbers less than 1000000 (asterisk marks primes):
     1       7*     23*     59*    119     191*    287     395     615     839*
  1079    1439*   1679    1931*   2391    3015    3479    3959    4619    5039*
  5615    6395    7215    8447*   9599   10199   10811   11447*  12095   14111 
 16379   17679   18767   20423   22199   23399*  25271   26891*  28551   30615 
 32039   34199   36479*  37631   38807   41579*  46619*  50171   51527   52895 
 55215   57119*  59999*  63999   67071   70215   72359   74519   77279*  78959 
 82343   89351   94859   96719   98591  104279  110879* 116255  120407  122495 
126015  131027  136151  140615  144395  148215  153647  158399  163199* 170543 
175559  180599  185759  189215  193595  198015  204287  209759  212519  215291 
222747  232307* 238139  244019  249995  255015  264159  271439  281879  294839 
303575  312471  319215  323759* 328319  337535  346911  354015  358799  363599 
370871* 376991  380687  389339  403199  410879  414731* 421191  429015  434279 
443519  454271  461031  470579* 482999  495599  508343  521267* 531431  540215 
547595  556499  566999* 574559  583679  592895  606791* 625655  643167  654479 
664199* 674039  678971* 683927  693863  713975  729311  734447  739595  755111 
770879  776159* 781451  802715  824459* 835379* 851903  868607  879839* 889239 
900591  919631* 937019  946719  958431  972179  986039

Wren

Library: Wren-math
Library: Wren-seq
Library: Wren-fmt

<lang ecmascript>import "/math" for Int import "/seq" for Lst import "/fmt" for Fmt

var primes = Int.primeSieve(101) var frobenius = [] for (i in 0...primes.count-1) { 

   var frob = primes[i]*primes[i+1] - primes[i] - primes[i+1]
   if (frob >= 10000) break
   frobenius.add(frob)

} System.print("Frobenius numbers under 10,000:") for (chunk in Lst.chunks(frobenius, 9)) Fmt.print("$,5d", chunk) System.print("\n%(frobenius.count) such numbers found.")</lang>

Output:
Frobenius numbers under 10,000:
    1     7    23    59   119   191   287   395   615
  839 1,079 1,439 1,679 1,931 2,391 3,015 3,479 3,959
4,619 5,039 5,615 6,395 7,215 8,447 9,599

25 such numbers found.
Retrieved from "https://rosettacode.org/wiki/Frobenius_numbers?oldid=310593"