Originally Posted By: Mathboy
"Mum, is One prime number too?"
"Probably not"
"Why??"
"Hum...you got me, I don't know."

Don't know if you're actually looking for an answer to that question, but here it is anyway! laugh

One used to be considered a prime until pretty recently in the history of math. It turns out that various things (including the "fundamental theorem of arithmetic") work out more neatly if you define the primes to not include 1. Wikipedia sez: "the prime numbers have several properties that the number 1 lacks," so excluding 1 is the more sensible, natural definition of the primes.

Makes me want to smack the math teachers who told us smugly, "It's because a prime has exactly two different divisors, 1 and itself." And then they would give us a "gotcha" look, like they expected us to be impressed with the profundity of this insight. They didn't get it that they were just repeating the definition, without any justification.