题解 | #完全数计算#

#include <cmath>
#include <iostream>
using namespace std;

int main() {
    int max_n;
    while (cin >> max_n) {
        int count = 0;
        for (int n = 2; n <= max_n; ++n) {
            int sum = 1;
            for (int i = 2; i <= sqrt(n); ++i) {
                if (n % i == 0) {
                    sum += i;
                    int tmp = n / i;
                    if (tmp != i) {
                        sum += tmp;
                    }
                }
            }
            if (sum == n) {
                ++count;
            }
        }
        cout << count << endl;
    }
}
// 64 位输出请用 printf("%lld")