C++ program to find n-th term of series 1, 3, 6, 10, 15, 21…

In this problem, we are given an integer N. The task is to find the n-th term in series 1, 3, 6, 10, 15, 21, 28....

Let’s take an example to understand the problem,


N = 7




The series is 1, 3, 6, 10, 15, 21, 28...

Solution Approach

A simple solution to the problem is by finding the general term of the series. On observing the series we can see that the ith number of the series is the sum of (i-1)th term and i.

This type of number is called triangular number.

To solve the problem, we will loop till n, and for each iteration add the current index with the last element’s value. At last return the Nth elements value.

Program to illustrate the working of our solution,


 Live Demo

#include <iostream>
using namespace std;
int findNthTerm(int N) {
   int NthTerm = 0;
   for (int i = 1; i <= N; i++)
      NthTerm = NthTerm + i;
   return NthTerm;
int main() {
   int N = 8;
   cout<<"The "<<N<<"th term of the series is "<<findNthTerm(N);
   return 0;


The 8th term of the series is 36

Updated on: 13-Mar-2021


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