Quote Originally Posted by Violyre View Post
Two, I learned primes are numbers that are only divisible by 1 and itself. Just because "itself" is also 1 doesn't change matters. It's divisible by 1 and 1, hence, prime.
1 is not prime because it would literally break all math involving prime numbers (which includes cryptography) if it were considered prime. Simplest example: Prime Factorization. Every integer n > 1 has a single unique prime factorization. If 1 is prime, then that falls apart because instead of 4 having a single prime factorization 2 * 2, it now has infinite prime factorizations 2 * 2 * 1^n for all n members of the counting numbers.