# Decagonal Numbers

You are given a number n, the task is to find the nth Decagonal number. A decagonal number is a figurate number that extends the concept of triangular and square numbers to the decagon (a ten-sided polygon). The nth decagonal numbers counts the number of dots in a pattern of n nested decagons, all sharing a common corner, where the ith decagon in the pattern has sides made of i dots spaced one unit apart from each other.

Examples:

```Input : n = 3
Output : 27

Input : n = 7
Output : 175
```

The n-th decagonal number is given by the formula
(4n 2 – 3n).

## C++

 `// C++ program to find nth decagonal number ` `#include ` `using` `namespace` `std; ` `  `  `// Function to calculate decagonal number ` `int` `decagonal(``int` `n) ` `{ ` `    ``// Formula for finding nth decagonal number ` `    ``return` `4 * n * n - 3 * n; ` `} ` `  `  `// Driver function ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << n << ``"th decagonal number :"` `<< decagonal(n); ` `    ``return` `0; ` `} `

## Java

 `// JAVA Code for Decagonal Numbers ` `import` `java.util.*; ` ` `  `class` `GFG { ` ` `  `    ``// Function to calculate  ` `    ``// decagonal number ` `    ``static` `int` `decagonal(``int` `n)  ` `    ``{ ` `        ``// Formula for finding nth ` `        ``// decagonal number ` `        ``return` `4` `* n * n - ``3` `* n; ` `    ``} ` `     `  `    ``/* Driver function */` `    ``public` `static` `void` `main(String[] args)  ` `    ``{     ` `        ``int` `n = ``10``; ` `        ``System.out.println(n + ``"th decagonal number :"` `                            ``+ decagonal(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by Arnav Kr. Mandal. `

## Python

 `# Python program to find nth decagonal number ` `def` `decagonal(n): ` `    ``return` `4` `*` `n ``*` `n ``-` `3` `*` `n ` `  `  `# Driver code ` `n ``=` `10` `print``(n, ``"th decagonal number :"``, decagonal(n)) `

## C#

 `// C# Code for Decagonal Numbers ` `using` `System; ` ` `  `class` `GFG { ` ` `  `    ``// Function to calculate  ` `    ``// decagonal number ` `    ``static` `int` `decagonal(``int` `n)  ` `    ``{ ` `        ``// Formula for finding nth ` `        ``// decagonal number ` `        ``return` `4 * n * n - 3 * n; ` `    ``} ` `     `  `    ``// Driver Code ` `    ``public` `static` `void` `Main()  ` `    ``{  ` `        ``int` `n = 10; ` `        ``Console.Write(n + ``"th decagonal number : "`  `                                   ``+ decagonal(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m. `

## PHP

 ` `

Output:

```10th decagonal number : 370
```

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