$=\dfrac{n(n+1)(2n+1)}{6}+\dfrac{n(n+1)}{2}$
by ez_lcw @ 2020-10-18 16:28:17
分开，1+4+9+16+。。。+1+2+3+。。。
两个部分都有公式，分开计算就行了
by wangpengjia @ 2020-10-18 16:28:40
n(n+1)(n+2)/3
by 某珂学的蒟蒻 @ 2020-10-18 16:28:54
```cpp
#include<iostream>
using namespace std;
int main() {
int n,sum=0;
cin >> n;
for (int i = 1; i <= n; i++) {
sum += i * (i+ 1);
}
cout << sum;
return 0;
}
```
by 城头有平安 @ 2020-10-18 16:31:40