# Chiliagon Number

Given a number **N**, the task is to find **N ^{th}** chiliagon number.

A chiliagon number is class of figurate number. It has 1000 – sided polygon called chiliagon. The N-th chiliagon number countâ€™s the 1000 number of dots and all others dots are surrounding with a common sharing corner and make a pattern. The first few chiliagonol numbers are

1, 1000, 2997, 5992 …

**Examples:**

Input:N = 2Output:1000Explanation:

The second chiliagonol number is 1000.Input:N = 3Output:2997

**Approach:** The N-th chiliagon number is given by the formula:

- Nth term of s sided polygon =
- Therefore Nth term of 1000 sided polygon is

Below is the implementation of the above approach:

## C++

`// C++ program for above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Finding the nth chiliagon Number` `int` `chiliagonNum(` `int` `n)` `{` ` ` `return` `(998 * n * n - 996 * n) / 2;` `}` `// Driver Code` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `cout <<` `"3rd chiliagon Number is = "` ` ` `<< chiliagonNum(n);` ` ` `return` `0;` `}` `// This code is contributed by shivanisinghss2110` |

## C

`// C program for above approach` `#include <stdio.h>` `#include <stdlib.h>` `// Finding the nth chiliagon Number` `int` `chiliagonNum(` `int` `n)` `{` ` ` `return` `(998 * n * n - 996 * n) / 2;` `}` `// Driver program to test above function` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `printf` `(` `"3rd chiliagon Number is = %d"` `,` ` ` `chiliagonNum(n));` ` ` `return` `0;` `}` |

## Java

`// Java program for the above approach` `class` `GFG{` `// Finding the nth chiliagon number` `static` `int` `chiliagonNum(` `int` `n)` `{` ` ` `return` `(` `998` `* n * n - ` `996` `* n) / ` `2` `;` `}` `// Driver code` `public` `static` `void` `main(String[] args)` `{` ` ` `int` `n = ` `3` `;` ` ` `System.out.println(` `"3rd chiliagon Number is = "` `+` ` ` `chiliagonNum(n));` `}` `}` `// This code is contributed by rutvik_56` |

## Python3

`# Python3 program for above approach` `# Finding the nth chiliagon Number` `def` `chiliagonNum(n):` ` ` `return` `(` `998` `*` `n ` `*` `n ` `-` `996` `*` `n) ` `/` `/` `2` `;` `# Driver Code` `n ` `=` `3` `;` `print` `(` `"3rd chiliagon Number is = "` `,` ` ` `chiliagonNum(n));` `# This code is contributed by Akanksha_Rai` |

## C#

`// C# program for the above approach` `using` `System;` `class` `GFG{` `// Finding the nth chiliagon number` `static` `int` `chiliagonNum(` `int` `n)` `{` ` ` `return` `(998 * n * n - 996 * n) / 2;` `}` `// Driver code` `public` `static` `void` `Main()` `{` ` ` `int` `n = 3;` ` ` `Console.Write(` `"3rd chiliagon Number is = "` `+` ` ` `chiliagonNum(n));` `}` `}` `// This code is contributed by Akanksha_Rai` |

## Javascript

`<script>` `// javascript program for above approach` `// Finding the nth chiliagon Number` `function` `chiliagonNum( n)` `{` ` ` `return` `(998 * n * n - 996 * n) / 2;` `}` `// Driver code` `let n = 3;` `document.write(` `"3rd chiliagon Number is "` `+ chiliagonNum(n));` `// This code contributed by gauravrajput1` `</script>` |

**Output:**

3rd chiliagon Number is = 2997

**Time Complexity: **O(1)

**Auxiliary Space: **O(1)

**Reference:** https://en.wikipedia.org/wiki/Chiliagon