Octadecagonal Number

Given a number N, the task is to find the Nth Octadecagonal number.

An Octadecagonal number is a class of figurate numbers. It has 18 – sided polygon called Octadecagon. The Nth Octadecagonal number count’s the eighteen number of dots and all other dots are surrounding with a common sharing corner and make a pattern. The first few Octadecagonal numbers are 1, 18, 51, 100, 165, 246, 343 …

Examples:

Input: N = 2
Output: 18
Explanation:
The second octadecagonal number is 18.

Input: N = 6
Output: 246



Approach: The Nth Octadecagonal number is given by the formula:

Tn = (16n^2 - 14n)/2

Below is the implementation of the above approach:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to find Nth
// Octadecagonal number
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to find N-th
// Octadecagonal number
int Octadecagonal_num(int n)
{
    // Formula to calculate nth
    // Octadecagonal number
    return (16 * n * n - 14 * n) / 2;
}
  
// Driver code
int main()
{
    int n = 3;
    cout << Octadecagonal_num(n) << endl;
  
    n = 10;
    cout << Octadecagonal_num(n) << endl;
  
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to find Nth
// octadecagonal number
import java.io.*; 
import java.util.*; 
  
class GFG{ 
      
// Function to find N-th
// octadecagonal number
static int Octadecagonal_num(int n)
{
          
    // Formula to calculate nth
    // octadecagonal number
    return (16 * n * n - 14 * n) / 2;
}
      
// Driver code 
public static void main(String[] args) 
    int n = 3;
    System.out.println(Octadecagonal_num(n));
      
    n = 10;
    System.out.println(Octadecagonal_num(n));
  
// This code is contributed by coder001

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 program to find Nth 
# octadecagonal number
  
# Function to find N-th 
# octadecagonal number
def Octadecagonal_num(n):
      
    # Formula to calculate nth 
    # octadecagonal number 
    return (16 * n * n - 14 * n) / 2
  
# Driver code    
n = 3
print(int(Octadecagonal_num(n))) 
  
n = 10
print(int(Octadecagonal_num(n))) 
  
# This code is contributed by divyeshrabadiya07     

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to find Nth
// octadecagonal number
using System; 
  
class GFG{ 
      
// Function to find N-th
// octadecagonal number
static int Octadecagonal_num(int n)
{
          
    // Formula to calculate nth
    // octadecagonal number
    return (16 * n * n - 14 * n) / 2;
}
      
// Driver code 
public static void Main(string[] args) 
    int n = 3;
    Console.Write(Octadecagonal_num(n) + "\n");
      
    n = 10;
    Console.Write(Octadecagonal_num(n) + "\n");
  
// This code is contributed by rutvik_56

chevron_right


Output:

51
730

Reference: https://en.wikipedia.org/wiki/Polygonal_number

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.




My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.