# Find the nth term of the given series

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: 1

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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

 ` `

Output:

```15
```

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