my $num = "000";
{
  $num =~ s{(^|.)(z*)$}{
    my ($left, $right) = ($1, $2);
    $left =~ tr/0-9a-y/1-9a-z/ or $left = "10";
    $right =~ tr/z/0/;
    $left . $right;
  }e;
  print "$num\n";
  redo while length $num < 20;
}