# Find the nth term of the given series

• Last Updated : 07 Jun, 2022

Given the first two terms of the series as 1 and 6 and all the elements of the series are 2 less than the mean of the number preceding and succeeding it. The task is to print the nth term of the series.
First few terms of the series are:

1, 6, 15, 28, 45, 66, 91, …

Examples:

Input: N = 3
Output: 15
Input: N = 1
Output:

Approach: The given series represents odd positioned numbers in the triangular number series. Since the nth triangular number can easily be found by (n * (n + 1) / 2), so for finding the odd numbers we can replace n by (2 * n) – 1 as (2 * n) – 1 will always result in odd numbers i.e. the nth number of the given series will be ((2 * n) – 1) * n.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the nth term``// of the given series``int` `oddTriangularNumber(``int` `N)``{``    ``return` `(N * ((2 * N) - 1));``}` `// Driver code``int` `main()``{``    ``int` `N = 3;``    ``cout << oddTriangularNumber(N);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``class` `GFG``{` `// Function to return the nth term``// of the given series``static` `int` `oddTriangularNumber(``int` `N)``{``    ``return` `(N * ((``2` `* N) - ``1``));``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `N = ``3``;``    ``System.out.println(oddTriangularNumber(N));``}``}` `// This code contributed by Rajput-Ji`

## Python3

 `# Python 3 implementation of the approach` `# Function to return the nth term``# of the given series``def` `oddTriangularNumber(N):``    ``return` `(N ``*` `((``2` `*` `N) ``-` `1``))` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``N ``=` `3``    ``print``(oddTriangularNumber(N))` `# This code is contributed by``# Surendra_Gangwar`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{` `    ``// Function to return the nth term``    ``// of the given series``    ``static` `int` `oddTriangularNumber(``int` `N)``    ``{``        ``return` `(N * ((2 * N) - 1));``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``int` `N = 3;``        ``Console.WriteLine(oddTriangularNumber(N));``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## PHP

 ``

## Javascript

 ``

Output:

`15`

Time Complexity: O(1)

Auxiliary Space: O(1)

My Personal Notes arrow_drop_up