Question

Which of these numbers is a prime number: 1, 11, 21, 51?

Answer 1

11 and 51

Explanation:

1 technically isn't a prime since a prime can only be divided by two things (itself and 1) and 1 can only be divided by 1.

21 can be divided by 1, 3, 7, and 21 so it is not prime.

Hope this helps!