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 <bits/stdc++.h>` `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

`<?php` `// PHP program to find nth` `// decagonal number` `// Function to calculate` `// decagonal number` `function` `decagonal(` `$n` `)` `{` ` ` ` ` `// Formula for finding nth` ` ` `// decagonal number` ` ` `return` `4 * ` `$n` `* ` `$n` `- 3 * ` `$n` `;` `}` `// Driver function` `$n` `= 10;` `echo` `$n` `, ` `"th decagonal number :"` `,` ` ` `decagonal(` `$n` `);` `// This code is contributed by ajit` `?>` |

## Javascript

`<script>` `// JavaScript program for Decagonal Numbers` `// Function to calculate` `// decagonal number` `function` `decagonal(n)` `{` ` ` ` ` `// Formula for finding nth` ` ` `// decagonal number` ` ` `return` `4 * n * n - 3 * n;` `}` `// Driver code` `let n = 10;` `document.write(n + ` `"th decagonal number : "` `+` ` ` `decagonal(n));` ` ` `// This code is contributed by souravghosh0416` `</script>` |

**Output: **

10th decagonal number : 370

Attention reader! Don’t stop learning now. Get hold of all the important mathematical concepts for competitive programming with the **Essential Maths for CP Course** at a student-friendly price. To complete your preparation from learning a language to DS Algo and many more, please refer **Complete Interview Preparation Course****.**