Desafio Geek - Perl v1

#!/usr/bin/perl

use strict;
use warnings;

use POSIX;

my $regexp = '(\d)(\d)(\d)(\d)(\3)(\2)(\1)';
my $sqrt = 0;
my $palindrome;
my $counter;

if(defined($ARGV[0])){
    $regexp = "";
    for($counter = 0; $counter < $ARGV[0];$counter++){
        if($counter > ceil($ARGV[0]/2)-1){
            $regexp .= "(\\".($ARGV[0]-$counter).")";
        }else{
            $regexp .= "(\\d)";
        }
    }
}




while(read){
    while ($_ =~ /$regexp/g) {
        $palindrome = $&;;

        #print $palindrome."\n";

        if($palindrome % 2 == 0){
            next;
        }

        $sqrt = sqrt($palindrome);
        for($counter = 3; $counter <= $sqrt; $counter+=2){
            if($palindrome % $counter == 0){
                last;
            }
        }
        if($counter >  $sqrt){
            print $palindrome."\n";
        }
    }
}