题解 | #等差数列#

//使用等差数列求和公式Sn=((A1+An)n)/2,本题中An=n3-1，A1=2.

#include<iostream>
using namespeace std;

int main(){
    int n;
    while(cin >> n){
        int lastnum = n * 3 - 1;
        cout << ((2 + lastnum)*n) / 2 << endl;
    }
    return 0;   
}