Question

How many positive integers less than 20 have exactly 2 positive divisors?

Answer 1

7 numbers

2 , 3 , 5 , 7 , 11 , 13 , 17 , 19

Explanation:

Only a prime number has exactly 2 positive divisors which are 1 and himself

and the prime numbers less than 20 are : 2 , 3 , 5 , 7 , 11 , 13 , 17 , 19