递推

C++ 代码

#include <iostream>

using namespace std;
const int N = 1e6+10;
int f[N];
const int MOD = 998244353;

int main() {
    int n;
    cin >> n;
    f[1] = 0;
    int p = 1; // 代表阶乘
    for (int i = 1; i < n; ++i) {
        p = 1ll * p * i % MOD;
        f[i + 1] = (1ll * i * (i + 1) / 2  * p  + 1ll * f[i] * (i + 1) )% MOD;
        f[i + 1] %= MOD; 
    }
    cout << f[n] << '\n';
    return 0;
}