#include<bits/stdc++.h>

#define int unsigned long

using namespace std;

int GT(int n)

 {

    if (n == 0 || n == 1) return 1;

    else return n * GT(n - 1);

}

signed main() 

{

  ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

    int a, b, s = 0; cin >> a >> b;

    for (int i = a; i <= b; i ++) s += GT(i);

    cout << s;

}

Code C++ : 

#include<bits/stdc++.h>
#define ll long long
using namespace std;
unsigned  ll qq(ll n)
 {
    if (n == 0 || n == 1)
    {
        return 1;
    }
    else
        return n * qq(n - 1);
}

int main() {
    unsigned  ll a, b,tt=0;
    cin >> a;
    cin >> b;
    for (ll num = a; num <= b; num++)
    {
        tt+= qq(num);
    }
    cout << "tổng giai thừa từ a đến b là :  "  << tt << endl;
    return 0;
}