^.?$|^(..+?)\1+$
<answer>
Matches strings of any character repeated a non-prime number of times
7 points
Yeah, I was younger then, perhaps less disciplined, and as always, given enough work you can decompile or regenerate anything. Still, I contend, the nature of Perl, powerful as it was, lent itself to unmaintainable messes, and I’m not talking regex’s, which is why it has faded, no amount of get gud withstanding.