Hello pvfki,

Your script has a number of problems:

• The forprimes function must be explicitly imported: e.g., use ntheory 'forprimes';.
• forprimes takes a block followed by either 1 or 2 integers.
• Within the block, the current prime is assigned to $_ ($p always remains 100).
• In the expression grep {!/$remove/} @candidates the regex matches any string containing the characters in $remove. So, e.g., if $remove is 1 then the regex will match 10. To fix this, you can add a beginning-of-string and an end-of-string assertion: grep {!/^$remove$/} .... However, it’s simpler to use != here: grep { $_ != $remove } @candidates.
• There is no real point in calling sieve2() twice. Since you don’t pass @candidates into the function, it will be set by the first call and unchanged by subsequent calls.

I think the following code is what you’re looking for:

use warnings;
use strict;
use ntheory 'forprimes';
use bigint;

my $n =  12;
my $c =   1;
my $k =  10;
my $l =  10;
my $p = 100;
my @candidates = (0 .. $l);
my $remove;

sieve2();

sub sieve2
{
    forprimes
    {
        for my $i (0 .. $l)
        {
            if (($n * ($k + $i) + $c) % $_ == 0)
            {
                $remove = $i;
                @candidates = grep { $_ != $remove } @candidates;
            }
        }
    }

    $p;

    print join("\n", @candidates),"\n";
}
[download]

Output:

16:58 >perl 2012_SoPW.pl
3
5
6
9
10

16:58 >
[download]

Hope that helps,

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