Which of the following is NOT a prime number?  Choose the correct choice from the following answers:	A) 21	B) 31	C) 41	D) 11	E) 51
Ans is A   A prime number has itself and 1 as the only factors. e.g. 2, 3, 7, 11, 19. Factors of 21 = {1 , 3 , 7 , 21} =&gt; 21 is not a prime number
<result>A</result>
Which of the following is NOT a prime number?