sub mklist {
    my $num = shift;
    return "1" if $num == 1;
    return ($num,(map {$_,$_.$num} mklist($num-1)));
}

print join "\n", mklist(5);
print "\n";
__END__
5
4
45
3
35
34
345
2
25
24
245
23
235
234
2345
1
15
14
145
13
135
134
1345
12
125
124
1245
123
1235
1234
12345