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

An Icosioctagon number is class of figurate number. It has 28 – sided polygon called icosikaioctagon. The N-th icosikaioctagonal number count’s the 28 number of dots and all others dots are surrounding with a common sharing corner and make a pattern. The first few icosikaioctagonol numbers are

1, 28, 81, 160 …

**Examples:**

Input:N = 2

Output:28

Explanation:

The second icosikaioctagonol number is 28.

Input:N = 3

Output:81

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

- Nth term of s sided polygon =
- Therefore Nth term of 28 sided polygon is

Below is the implementation of the above approach:

## C++

`// C++ program for above approach ` `#include <iostream> ` `using` `namespace` `std; ` ` ` `// Finding the nth icosikaioctagonal number ` `int` `icosikaioctagonalNum(` `int` `n) ` `{ ` ` ` `return` `(26 * n * n - 24 * n) / 2; ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `int` `n = 3; ` ` ` ` ` `cout << ` `"3rd icosikaioctagonal Number is = "` ` ` `<< icosikaioctagonalNum(n); ` ` ` ` ` `return` `0; ` `} ` ` ` `// This code is contributed by shubhamsingh10 ` |

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## C

`// C program for above approach ` `#include <stdio.h> ` `#include <stdlib.h> ` ` ` `// Finding the nth icosikaioctagonal Number ` `int` `icosikaioctagonalNum(` `int` `n) ` `{ ` ` ` `return` `(26 * n * n - 24 * n) / 2; ` `} ` ` ` `// Driver program to test above function ` `int` `main() ` `{ ` ` ` `int` `n = 3; ` ` ` `printf` `(` `"3rd icosikaioctagonal Number is = %d"` `, ` ` ` `icosikaioctagonalNum(n)); ` ` ` ` ` `return` `0; ` `} ` |

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## Java

`// Java program for above approach ` `class` `GFG{ ` ` ` `// Finding the nth icosikaioctagonal number ` `public` `static` `int` `icosikaioctagonalNum(` `int` `n) ` `{ ` ` ` `return` `(` `26` `* n * n - ` `24` `* n) / ` `2` `; ` `} ` ` ` `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` ` ` `int` `n = ` `3` `; ` ` ` `System.out.println(` `"3rd icosikaioctagonal Number is = "` `+ ` ` ` `icosikaioctagonalNum(n)); ` `} ` `} ` ` ` `// This code is contributed by divyeshrabadiya07 ` |

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## Python3

`# Python3 program for above approach ` ` ` `# Finding the nth icosikaioctagonal Number ` `def` `icosikaioctagonalNum(n): ` ` ` ` ` `return` `(` `26` `*` `n ` `*` `n ` `-` `24` `*` `n) ` `/` `/` `2` ` ` `# Driver Code ` `n ` `=` `3` `print` `(` `"3rd icosikaioctagonal Number is = "` `, ` ` ` `icosikaioctagonalNum(n)) ` ` ` `# This code is contributed by divyamohan123 ` |

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## C#

`// C# program for above approach ` `using` `System; ` `class` `GFG{ ` ` ` `// Finding the nth icosikaioctagonal number ` `public` `static` `int` `icosikaioctagonalNum(` `int` `n) ` `{ ` ` ` `return` `(26 * n * n - 24 * n) / 2; ` `} ` ` ` `// Driver code ` `public` `static` `void` `Main() ` `{ ` ` ` `int` `n = 3; ` ` ` `Console.Write(` `"3rd icosikaioctagonal Number is = "` `+ ` ` ` `icosikaioctagonalNum(n)); ` `} ` `} ` ` ` `// This code is contributed by Code_Mech ` |

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**Output:**

3rd icosikaioctagonal Number is = 81

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

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