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• Last Updated : 13 Jul, 2021

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

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  functionint center_octadecagon_num(long int n){    // Formula to calculate nth    // centered octadecagonal number    return 9 * n * n - 9 * n + 1;} // Driver Codeint 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// numberimport java.io.*; class GFG{     // centered octadecagon functionstatic int center_octadecagon_num(int n){             // Formula to calculate nth    // centered octadecagonal number    return 9 * n * n - 9 * n + 1;} // Driver Codepublic 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 functiondef center_octadecagon_num(n) :         # Formula to calculate    # nth centered octadecagonal    # number & return it    # into main function.    return(9 * n * n -           9 * n + 1) # Driver Codeif __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// numberusing System; class GFG{     // centered octadecagon functionstatic int center_octadecagon_num(int n){             // Formula to calculate nth    // centered octadecagonal number    return 9 * n * n - 9 * n + 1;} // Driver Codestatic 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.



Javascript



Output :

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

Time Complexity: O(1)
Auxiliary Space: O(1)

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