# Find the nth term of the given series

• Last Updated : 08 Apr, 2021

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

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## Javascript

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Output:

`15`

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