The definition I usually use (speaking loosely for the moment) is that prime numbers are natural numbers greater than one whose divisors are only one and itself

The definition I usually use (speaking loosely for the moment) is that prime numbers are natural numbers greater than one whose divisors are only one and itself. Speaking more formally, a natural number p is a prime if and only if: a) p > 1 b) for any natural number n satisfying 1 < n < p, p mod n ≠ 0