# Icosihenagonal Number

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

An Icosihenagonal number is class of figurate number. It has 21 – sided polygon called Icosihenagon. The n-th Icosihenagonal number counts the 21 number of dots and all others dots are surrounding with a common sharing corner and make a pattern. The first few Icosihenagonal numbers are 1, 21, 60, 118, 195, 291, 406 …

Examples:

Input: N = 2
Output: 21
Explanation:
The second Icosihenagonal number is 21

Input: N = 6
Output: 291

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

``` ```

Below is the implementation of the above approach:

## C++

 `// C++ program to find nth ` `// Icosihenagonal number ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to find ` `// Icosihenagonal number ` `int` `Icosihenagonal_num(``int` `n) ` `{ ` `    ``// Formula to calculate nth ` `    ``// Icosihenagonal number ` `    ``return` `(19 * n * n - 17 * n) / 2; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `n = 3; ` `    ``cout << Icosihenagonal_num(n) << endl; ` ` `  `    ``n = 10; ` `    ``cout << Icosihenagonal_num(n) << endl; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to find nth ` `// Icosihenagonal number ` `class` `GFG{ ` ` `  `// Function to find ` `// Icosihenagonal number ` `static` `int` `Icosihenagonal_num(``int` `n) ` `{ ` `    ``// Formula to calculate nth ` `    ``// Icosihenagonal number ` `    ``return` `(``19` `* n * n - ``17` `* n) / ``2``; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `n = ``3``; ` `    ``System.out.print(Icosihenagonal_num(n) + ``"\n"``); ` ` `  `    ``n = ``10``; ` `    ``System.out.print(Icosihenagonal_num(n) + ``"\n"``); ` `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Python3

 `# Python3 program to find nth  ` `# icosihenagonal number  ` ` `  `# Function to find  ` `# icosihenagonal number  ` `def` `Icosihenagonal_num(n): ` `     `  `    ``# Formula to calculate nth  ` `    ``# icosihenagonal number ` `    ``return` `(``19` `*` `n ``*` `n ``-` `17` `*` `n) ``/` `2` `     `  `# Driver Code ` `n ``=` `3` `print``(``int``(Icosihenagonal_num(n))) ` ` `  `n ``=` `10` `print``(``int``(Icosihenagonal_num(n))) ` ` `  `# This code is contributed by divyeshrabadiya07 `

## C#

 `// C# program to find nth ` `// Icosihenagonal number ` `using` `System; ` ` `  `class` `GFG{ ` ` `  `// Function to find ` `// Icosihenagonal number ` `static` `int` `Icosihenagonal_num(``int` `n) ` `{ ` `    ``// Formula to calculate nth ` `    ``// Icosihenagonal number ` `    ``return` `(19 * n * n - 17 * n) / 2; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `Main() ` `{ ` `    ``int` `n = 3; ` `    ``Console.Write(Icosihenagonal_num(n) + ``"\n"``); ` ` `  `    ``n = 10; ` `    ``Console.Write(Icosihenagonal_num(n) + ``"\n"``); ` `} ` `} ` ` `  `// This code is contributed by Code_Mech `

Output:

```60
865
```

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