# Hendecagonal number

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

Examples:

Input : 2
Output :11

Input :6
Output :141 Formula for nth hendecagonal number : ## C++

 // C++ program to find nth  // Hendecagonal number  #include  using namespace std;     // Function to find  // Hendecagonal number  int hendecagonal_num(int n)  {      // Formula to calculate nth      // Hendecagonal number      return (9 * n * n - 7 * n) / 2;  }     // Driver Code  int main()  {      int n = 3;      cout << n << "rd Hendecagonal number: ";      cout << hendecagonal_num(n);      cout << endl;      n = 10;      cout << n << "th Hendecagonal number: ";      cout << hendecagonal_num(n);         return 0;  }

## Java

 // Java program to find nth  // Hendecagonal number  import java.io.*;     class GFG  {         // Function to find  // Hendecagonal number  static int hendecagonal_num(int n)  {      // Formula to calculate nth      // Hendecagonal number      return (9 * n * n -               7 * n) / 2;  }     // Driver Code  public static void main (String[] args)  {  int n = 3;  System.out.print(n + "rd Hendecagonal " +                               "number: ");  System.out.println(hendecagonal_num(n));     n = 10;  System.out.print(n + "th Hendecagonal " +                                "number: ");  System.out.println(hendecagonal_num(n));  }  }     // This code is contributed by ajit

## Python3

 # Program to find nth  # Hendecagonal number     # Function of Hendecagonal   # number   def hendecagonal_num(n) :             # Formula to calculate nth      # Hendecagonal number &      # return it into main function.             return (9 * n * n -             7 * n) // 2    # Driver Code  if __name__ == '__main__' :                 n = 3     print(n,"rd Hendecagonal number : " ,                       hendecagonal_num(n))         n = 10     print(n,"th Hendecagonal number : " ,                       hendecagonal_num(n))     # This code is contributed by ajit

## C#

 // C# program to find nth  // Hendecagonal number  using System;     class GFG  {  // Function to find  // Hendecagonal number  static int hendecagonal_num(int n)  {      // Formula to calculate nth      // Hendecagonal number      return (9 * n * n - 7 * n) / 2;  }     // Driver Code  static public void Main ()  {      int n = 3;      Console.Write(n +                    "rd Hendecagonal number: ");      Console.WriteLine( hendecagonal_num(n));         n = 10;      Console.Write(n +                    "th Hendecagonal number: ");      Console.WriteLine( hendecagonal_num(n));      }  }     // This code is contributed by aj_36

## PHP

 

Output :

3th Hendecagonal number: 30
10th Hendecagonal number: 415


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