Which of the following numbers are prime?

4

5

6

7

Factors of 4: 1, 2, 4

Factors of 5: 1, 5

Factors of 6: 1, 2, 3, 6

Factors of 7: 1, 7

Since factors of 5 and 7 are 1 and itself, 5 and 7 are prime