思路:
找规律。
实现:
1 #include <bits/stdc++.h> 2 using namespace std; 3 typedef long long ll; 4 int main() 5 { 6 ll n; 7 while (cin >> n) 8 { 9 ll cnt = 0; 10 for (int i = 2; i * i <= n; i++) 11 { 12 ll tmp = n / i; 13 cnt += (i + 1 + tmp) * (tmp - i) / 2; 14 cnt += (tmp - i + 1) * i; 15 } 16 cout << (cnt << 2) << endl; 17 } 18 return 0; 19 }