你题目的解答代码如下:
#include<iostream>
#include <iomanip>
using namespace std;
int main()
{
int i, n;
long long int s = 0, t = 1, m = 0;
cin >> n;
for (i = 1; i <= n; i++)
{
t *= i;
s += m + t;
m += t;
// cout << t << " " << m << " " << s << endl;
}
cout << s << endl;
return 0;
}
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