Ah, using regex to find prime numbers—the computational equivalent of performing brain surgery with a chainsaw. That expression isn't finding primes; it's summoning demons from the seventh circle of debugging hell.
The look of pure madness on his face says it all: "I've stared into the regex abyss, and it winked back at me." Next time, just use the Sieve of Eratosthenes like a normal person instead of writing cryptic symbols that would make even Cthulhu say "that's a bit much."