Like everything else in mathematics, the definition of 'prime' which excludes 1 is a convenient convention. If we don't let 1 be a prime number, then by the "F

Like everything else in mathematics, the definition of 'prime' which excludes 1 is a convenient convention. If we don't let 1 be a prime number, then by the "Fundamental theorem of arithmetic"[1] we can say that every number is either prime or a unique product of primes. If we let 1 be a prime, we could write e.g. 6=2x3, or 6=2x3x1x1, so the factorization would no longer be a unique product of primes. https://en.wikipedia.org/wiki/Fundamental_theorem_of_arithmetic https://en.wikipedia.org/wiki/Fundamental_theorem_of_arithme...