#include <iostream>
using namespace std;

//S = 1*2 + 2*3 + 3*4 + ...+ (n-1)*n

int DeQuy(int n)
{
	if (n == 2)
		return 2;
	return ((n - 1) * n) + DeQuy(n - 1);
}

int main()
{
	int n;
	cout << "Hay nhap n = ";
	cin >> n;
	cout << "\nKet qua = : " << DeQuy(n);
	system("pause");
	return 0;
}

Đáp án