Given a number N, the task is to find the Nth Octadecagonal number.

An Octadecagonal number is a class of figurate numbers. It has 18 – sided polygon called Octadecagon. The Nth Octadecagonal number count’s the eighteen number of dots and all other dots are surrounding with a common sharing corner and make a pattern. The first few Octadecagonal numbers are 1, 18, 51, 100, 165, 246, 343 …

Examples:

Input: N = 2
Output: 18
Explanation:
The second octadecagonal number is 18.

Input: N = 6
Output: 246

## Recommended: Please try your approach on {IDE} first, before moving on to the solution. Approach: The Nth Octadecagonal number is given by the formula:

``` ```

Below is the implementation of the above approach:

## C++

 `// C++ program to find Nth ` `// Octadecagonal number ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to find N-th ` `// Octadecagonal number ` `int` `Octadecagonal_num(``int` `n) ` `{ ` `    ``// Formula to calculate nth ` `    ``// Octadecagonal number ` `    ``return` `(16 * n * n - 14 * n) / 2; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 3; ` `    ``cout << Octadecagonal_num(n) << endl; ` ` `  `    ``n = 10; ` `    ``cout << Octadecagonal_num(n) << endl; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to find Nth ` `// octadecagonal number ` `import` `java.io.*;  ` `import` `java.util.*;  ` ` `  `class` `GFG{  ` `     `  `// Function to find N-th ` `// octadecagonal number ` `static` `int` `Octadecagonal_num(``int` `n) ` `{ ` `         `  `    ``// Formula to calculate nth ` `    ``// octadecagonal number ` `    ``return` `(``16` `* n * n - ``14` `* n) / ``2``; ` `} ` `     `  `// Driver code  ` `public` `static` `void` `main(String[] args)  ` `{  ` `    ``int` `n = ``3``; ` `    ``System.out.println(Octadecagonal_num(n)); ` `     `  `    ``n = ``10``; ` `    ``System.out.println(Octadecagonal_num(n)); ` `}  ` `}  ` ` `  `// This code is contributed by coder001 `

## Python3

 `# Python3 program to find Nth  ` `# octadecagonal number ` ` `  `# Function to find N-th  ` `# octadecagonal number ` `def` `Octadecagonal_num(n): ` `     `  `    ``# Formula to calculate nth  ` `    ``# octadecagonal number  ` `    ``return` `(``16` `*` `n ``*` `n ``-` `14` `*` `n) ``/` `2` ` `  `# Driver code     ` `n ``=` `3` `print``(``int``(Octadecagonal_num(n)))  ` ` `  `n ``=` `10` `print``(``int``(Octadecagonal_num(n)))  ` ` `  `# This code is contributed by divyeshrabadiya07      `

## C#

 `// C# program to find Nth ` `// octadecagonal number ` `using` `System;  ` ` `  `class` `GFG{  ` `     `  `// Function to find N-th ` `// octadecagonal number ` `static` `int` `Octadecagonal_num(``int` `n) ` `{ ` `         `  `    ``// Formula to calculate nth ` `    ``// octadecagonal number ` `    ``return` `(16 * n * n - 14 * n) / 2; ` `} ` `     `  `// Driver code  ` `public` `static` `void` `Main(``string``[] args)  ` `{  ` `    ``int` `n = 3; ` `    ``Console.Write(Octadecagonal_num(n) + ``"\n"``); ` `     `  `    ``n = 10; ` `    ``Console.Write(Octadecagonal_num(n) + ``"\n"``); ` `}  ` `}  ` ` `  `// This code is contributed by rutvik_56 `

Output:

```51
730
```

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