# Icosidigonal number

Given a number n, the task is to find the nth Icosidigonal number (Isdn).
The polygon has the many gons, depends on their gonal number series. In mathematics, there is a number of gonal numbers and the icosidigonal number is one of them and these numbers have 22 -sided polygon (icosidigon). An icosidigonal number belong to the class of figurative number. They have one common dots points and other dots pattern is arranged in an n-th nested icosidigon pattern.

Examples :

Input : 2
Output :22

Input :6
Output :306 Formula for nth Icosidigonal number: ## C++

 // C++ program to find nth Icosidigonal  // number  #include  using namespace std;     // Function to calculate Icosidigonal number  int icosidigonal_num(long int n)  {      // Formula for finding      // nth Icosidigonal number      return (20 * n * n - 18 * n) / 2;  }     // Driver function  int main()  {      long int n = 4;      cout << n << "th Icosidigonal number :" << icosidigonal_num(n);      cout << endl;      n = 8;      cout << n << "th Icosidigonal number:" << icosidigonal_num(n);      return 0;  }

## Java

 // Java program to find nth   // Icosidigonal number   import java.io.*;     class GFG   {             // Function to calculate       // Icosidigonal number      static int icosidigonal_num(int n)       {                 // Formula for finding      // nth Icosidigonal number             return (20 * n * n - 18 * n) / 2;      }     // Driver Code  public static void main (String[] args)   {         int n = 4;      System.out.print (n + "th Icosidigonal number :");      System.out.println (icosidigonal_num(n));         n = 8;      System.out.print (n + "th Icosidigonal number :");      System.out.println (icosidigonal_num(n));  }  }     // This code is contributed by ajit

## Python 3

 # python 3 program to find   # nth Icosidigonal number     # Function to calculate  # Icosidigonal number  def icosidigonal_num(n) :             # Formula for finding      # nth Icosidigonal number      return (20 * n * n -              18 * n) // 2    # Driver Code  if __name__ == '__main__' :                 n = 4     print(n,"th Icosidigonal " +                     "number : ",               icosidigonal_num(n))      n = 8     print(n,"th Icosidigonal " +                     "number : ",               icosidigonal_num(n))         # This code is contributed m_kit

## C#

 // C# program to find nth   // Icosidigonal number   using System;     class GFG  {             // Function to calculate       // Icosidigonal number      static int icosidigonal_num(int n)       {                 // Formula for finding      // nth Icosidigonal number      return (20 * n * n -               18 * n) / 2;      }     // Driver Code  static public void Main ()  {  int n = 4;  Console.Write(n + "th Icosidigonal " +                            "number :");  Console.WriteLine(icosidigonal_num(n));     n = 8;  Console.Write (n + "th Icosidigonal "+                            "number :");  Console.WriteLine(icosidigonal_num(n));  }  }     // This code is contributed by ajit

## PHP

 

Output :

4th Icosidigonal number :124
8th Icosidigonal number:568


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Improved By : jit_t