Find total number of Rectangles (excluding squares) in a N*N cheesboard

#include<bits/stdc++.h>
using namespace std;

main()
{
    long long n;
    cin>>n;
    while(n--)
    {
        long long a;
        cin>>a;
        a=(((a*(a+1))/2)*((a*(a+1))/2))-((a*a+a)*(2*a+1))/6;
        cout<<a<<endl;
    }
}