How many integers in the set {1, 2 ,3......,100} have exactly 3 divisors?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 4.
A number has exactly 3 divisors if it is a square of a prime.
Find all squares of primes ≤ 100
Prime numbers ≤ 10 (since 112 = 121 > 100): 2, 3, 5, 7
Their squares: 4, 9, 25, 49 [4 numbers]