Ben's prime number joke

A man says he has come up with an algorithm for generating prime numbers -- all odd numbers are prime. Three ``experts'' are called in to verify this. All verify for different reasons:

mathematician

1, 3, 5, and 7 are prime, the rest by induction.

physicist

1, 3, 5, 7, 9 - experimental error, 11.

engineer

All odd numbers are prime.