Which of the following numbers are prime?
(a)   23   
(b) 51    
(c)  37    
(d) 26

Explanation

A prime number is a positive integer having exactly two factors. If p is a prime, then the only factors it can have are 1 and p. Any number that does not fall into this category is said to as a composite number, meaning it may be factored into other positive integers.


(a) 23
23 is a prime number since it contains just two factors: 1 and 23.


(b) 51
51 is not a prime number since it has 1, 3, 17, and 51.


(c) 37
37 is a prime number since it has both 1 and 37.


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