22 has factors of 1, 2, 11, 21, so it is a composite number.
15 has factors of 1, 3, 5, 14, so it is a composite number.
13 has factors of 1, 13, so it is a prime number.
12 has factors of 1, 2, 3, 4, 6, 12, so it is a composite number.
13 is the only prime number in this set.
