Four Divisors
<p>Given an integer array <code>nums</code>, return <em>the sum of divisors of the integers in that array that have exactly four divisors</em>. If there is no such integer in the array, return <code>0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [21,4,7]
<strong>Output:</strong> 32
<strong>Explanation:</strong> 
21 has 4 divisors: 1, 3, 7, 21
4 has 3 divisors: 1, 2, 4
7 has 2 divisors: 1, 7
The answer is the sum of divisors of 21 only.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [21,21]
<strong>Output:</strong> 64
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,4,5]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
</ul>
Array; Math
class Solution {
public:
    int sumFourDivisors(vector<int>& nums) {
        int ans = 0;
        for (int x : nums) {
            ans += f(x);
        }
        return ans;
    }

    int f(int x) {
        int cnt = 2, s = x + 1;
        for (int i = 2; i <= x / i; ++i) {
            if (x % i == 0) {
                ++cnt;
                s += i;
                if (i * i != x) {
                    ++cnt;
                    s += x / i;
                }
            }
        }
        return cnt == 4 ? s : 0;
    }
};