I've been factoring numbers on sight since I was eight years old, when a nice teacher taught me about primes. It's not so much that I enjoy it as that I feel a compulsion to make numbers into smaller simpler numbers.
One day I was on the #28 route, which that day was bus #2310. 2 x 3 x 5 x 7 x 11. The first five consecutive primes multiplied. Straight out of 2001, where primes are how Bowman shows the monolith that we're smart enough as a species to... advance and follow.