Pseudoprime Memes

The young man just committed the cardinal sin of number theory. 1387 is a Fermat pseudoprime - it looks prime but isn't (it's actually 7 × 11 × 18). Like claiming to enjoy math but not knowing your primes, it's the numerical equivalent of saying your favorite band is "The Led Zeppelins." Dad's countdown is mathematically justified. Some relationships just can't be factored into something that works.