$primecount = 0;
while ($primecount < 8) {
  $i++;
  print "$i\n" if ($i % 10000 == 0);
  next if (! (isprime($i)));
  $primecount = countprimes($i);
}
print "Stopped at $i (primecount = $primecount)\n";
exit;

sub countprimes {
  my $x = shift;
  my @crossed = ();
  my $c = 1;
  for ($j = 0; $j < length($x); $j++) {
    $m = substr($x,$j,1);
    next if ($crossed[$m] || ($x !~ $m));
	$crossed[$m] = 1;
	$d = 1;
	for ($k = 0; $k < 10; $k++) {
	  next if ($k == $m);
	  $n = $x;
	  $n =~ s/$m/$k/g;
	  $d++; if (isprime($n) && $n eq int($n));
	}
	$c = $d if ($d > $c);
  }
  return $c;
}

sub isprime {
    my $num = $_[0];
    my $val = 'prime';
    if ($num =~ /^\d+$/ && $num >= 2) {
        my $mod = 2;
        my $div = int sqrt $num;
        while ($mod <= $div) {
            ($num % $mod) == 0 ? ($val = 'composite', last) : $mod++;
        }
    } else { $val = 'neither'; }
    if ($val eq 'prime') {
      return 1;
    } else {
      return 0;
    }
}