27
27
27 and 31 are prime.
17, 23 and 31 are prime. 39 is not.
17, 23 and 31 are prime. 39 is not.
17, 19, 23, 29 and 31 are prime. 15, 21, 25 and 27 are composite..
29
29
51 is not a prime number: 3x17=51
39
41
Composite. Its prime factors are 23 and 31.
21 = 3x7 23 = prime 25 = 5x5 27 = 3x9 29 = prime 31 = prime 33 = 3x11 35 = 5x7 37 = prime 39 = 3x13