Centered Octadecagonal Number Last Updated : 29 Mar, 2023 Comments Improve Suggest changes Like Article Like Report Given a number n, find the nth Centered Octadecagonal number. The Centered Octadecagonal Number represents a dot in the center 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: CO_{n}= 9n^2 -9n+1 Below is the basic implementation of the above idea: C++ // C++ Program to find the // nth centered octadecagonal // number #include <bits/stdc++.h> 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; } C // C Program to find the // nth centered octadecagonal // number #include <stdio.h> // 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; printf("%ldth centered octadecagonal number : %d\n",n,center_octadecagon_num(n)); n = 13; printf("%ldth centered octadecagonal number : %d\n",n,center_octadecagon_num(n)); return 0; } // This code is contributed by kothavvsaakash. 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 <?php // PHP Program to find the // nth centered octadecagonal // number // centered octadecagon function function center_octadecagon_num($n) { // Formula to calculate nth // centered octadecagonal number return (9 * $n * $n - 9 * $n + 1); } // Driver Code $n = 3; echo $n , "th centered octadecagonal " . "number : ", center_octadecagon_num($n); echo "\n"; $n = 13; echo $n , "th centered octadecagonal " . "number : ", center_octadecagon_num($n); // This code is contributed by m_kit ?> JavaScript <script> // Javascript program to find the // nth centered octadecagonal // number // centered octadecagon function function center_octadecagon_num(n) { // Formula to calculate nth // centered octadecagonal number return 9 * n * n - 9 * n + 1; } // Driver Code var n = 3; document.write(n + "th centered " + "octadecagonal number : "); document.write(center_octadecagon_num(n) + "<br>"); n = 13; document.write(n + "th centered " + "octadecagonal number : "); document.write(center_octadecagon_num(n)); // This code is contributed by Kirti </script> Output : 3th centered octadecagonal number : 55 13th centered octadecagonal number : 1405 Time Complexity: O(1)Auxiliary Space: O(1) Comment More infoAdvertise with us Next Article Analysis of Algorithms J jit_t Follow Improve Article Tags : Mathematical Geometric DSA series Practice Tags : GeometricMathematicalseries Similar Reads Basics & PrerequisitesLogic Building ProblemsLogic building is about creating clear, step-by-step methods to solve problems using simple rules and principles. 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