Question: what has exactly two factors 1 and itself?
Answer: A prime number has exactly two factors, 1 and itself. For example, 13 is a prime number because the only factors of 13 are 1 and 13. The number 8 is not prime because it has four factors: 1, 2, 4 and 8. The number 1 is not a prime number because it only has one factor (itself).