A running joke that has been running on for far too long. Every profession has a different proof that all odd numbers are prime (and yes, we assume that 1 is prime, even though 1 is not prime):

- Mathematicians:
- "
*1 is prime, 3 is prime, 5 is prime, 7 is prime; the proof follows by induction*"
- Physicists:
- "
*1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is experimental error, 11 is prime, 13 is prime, 15 is experimental error, 17 is prime, 19 is prime; the empirical evidence is overwhelming.*"
- Engineers:
- "
*1 is odd, 3 is odd, 5 is odd, 7 is odd, 9 is odd, 11 is odd, 13 is odd, 15 is odd, 17 is odd, 19 is odd, ..., 111 is odd, ...*"
- Psychologists:
- "
*1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is latently prime but repressing it, 11 is prime, ...*"
- Computer scientists:
- "
*1 is prime, 3 is prime, 5 is prime, 7 is prime, 7 is prime, 7 is prime, 7 is prime, 7 is ...*"