Write a C++ program to Calculate the sum of the series (1) + (1+2) + (1+2+3) + (1+2+3+4) + ... + (1+2+3+4+...+n), where n is entered by the user.

Write a C++ program to Calculate the sum of the series (1) + (1+2) + (1+2+3) + (1+2+3+4) + ... + (1+2+3+4+...+n), where n is entered by the user.

Program Code:
#include <iostream>
using namespace std;
int main()
{
int n;
cout<<"Enter the value of n for the series : ";
cin>>n;
cout<<endl;
cout<<"Sum of (1) + (1+2) + (1+2+3) + (1+2+3+4) + ... + (1+2+3+4+...+n) series upto n terms is : "
cout << (n*(2+3*n+n*n))/6;
return 0;

}

The program output is tested on www.jdoodle.com
Output:
Enter the value of n for the series : 15
Sum of (1) + (1+2) + (1+2+3) + (1+2+3+4) + ... + (1+2+3+4+...+n) series upto n terms is : 680


Thanks
Gato (google+ user)
Mukesh Rajput