Question: is 1 a prime factor of 42?
Answer: The only way to write 42 as the product of primes (except to change the order of the factors) is 2 × 3 × 7. We call 2 × 3 × 7 the prime factorization of 42. ... In order to maintain this property of unique prime factorizations, it is necessary that the number one, 1, be categorized as neither prime nor composite.