Project Euler-6

Problem:

The sum of the squares of the first ten natural numbers is,

1 ² + 2 ² + ... + 10 ² = 385

The square of the sum of the first ten natural numbers is,

(1 + 2 + ... + 10) ² = 55 ² = 3025

Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025  385 = 2640.

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

This is a easy question and codes are as follows

#include <stdio.h>
#include <iostream>

using namespace std;

typedef long long ll;

int main() {
	ll ans = 0;
	for(ll i = 1; i <= 100; i++) {
		for(ll j = i+1; j <= 100; j++) {
			ans += i*j;
		}
	}
	ans *= 2;
	cout<< ans<< endl;
	return 0;
}