Given a number n, find the nth Centered Octadecagonal number.

The Centered Octadecagonal Number represents a dot in the centre and others dot are arranged around it in successive layers of octadecagon(18 sided polygon).

Examples :

Input :  2
Output : 19

Input : 6
Output : 271

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

In mathematics, Centered Octadecagonal number for n-th term is given by:

Below is the basic implementation of the above idea:

## C++

 // C++ Program to find the // nth centered octadecagonal // number #include using namespace std;    // centered octadecagon  function int center_octadecagon_num(long int n) {     // Formula to calculate nth     // centered octadecagonal number     return 9 * n * n - 9 * n + 1; }    // Driver Code int main() {     long int n = 3;     cout << n << "th centered octadecagonal number : "                   << center_octadecagon_num(n);     cout << endl;     n = 13;     cout << n << "th centered octadecagonal number : "                  << center_octadecagon_num(n);        return 0; }

## Java

 // Java Program to find the // nth centered octadecagonal // number import java.io.*;    class GFG  {        // centered octadecagon function static int center_octadecagon_num(int n) {                // Formula to calculate nth     // centered octadecagonal number     return 9 * n * n - 9 * n + 1; }    // Driver Code public static void main (String[] args)  { int n = 3; System.out.print(n + "th centered " +             "octadecagonal number : "); System.out.println(center_octadecagon_num(n));    n = 13; System.out.print(n + "th centered " +             "octadecagonal number : "); System.out.println(center_octadecagon_num(n)); } }    // This code is contributed by ajit

## Python3

 # Program to find nth # centered octadecagonal number    # Centered octadecagonal # number function def center_octadecagon_num(n) :            # Formula to calculate      # nth centered octadecagonal     # number & return it     # into main function.     return(9 * n * n -             9 * n + 1)    # Driver Code if __name__ == '__main__' :                n = 3     print(n,"rd centered octadecagonal " +                                 "number : ",                  center_octadecagon_num(n))        n = 13     print(n,"th centered octadecagonal " +                               "number : ",                  center_octadecagon_num(n))                # This code is contributed # by akt_mit

## C#

 // C# Program to find the // nth centered octadecagonal // number using System;    class GFG {        // centered octadecagon function static int center_octadecagon_num(int n) {                // Formula to calculate nth     // centered octadecagonal number     return 9 * n * n - 9 * n + 1; }    // Driver Code static public void Main () {            int n = 3;     Console.Write( n + "th centered " +              "octadecagonal number : ");     Console.WriteLine( center_octadecagon_num(n));        n = 13;     Console.Write( n + "th centered " +              "octadecagonal number : ");     Console.WriteLine(center_octadecagon_num(n)); } }    // This code is contributed by aj_36.

## PHP



Output :

3th centered octadecagonal number : 55
13th centered octadecagonal numbe : 1405

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Improved By : jit_t, ManasChhabra2