Given an integer n, return true if n has exactly three positive divisors. Otherwise, return false.
An integer m is a divisor of n if there exists an integer k such that n = k * m.
Example 1:
Input: n = 2 Output: false Explantion: 2 has only two divisors: 1 and 2.
Example 2:
Input: n = 4 Output: true Explantion: 4 has three divisors: 1, 2, and 4.
Constraints:
1 <= n <= 104