Octadecagonal Number
Last Updated :
18 Mar, 2021
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:
Below is the implementation of the above approach:
C++
#include <bits/stdc++.h>
using namespace std;
int Octadecagonal_num( int n)
{
return (16 * n * n - 14 * n) / 2;
}
int main()
{
int n = 3;
cout << Octadecagonal_num(n) << endl;
n = 10;
cout << Octadecagonal_num(n) << endl;
return 0;
}
|
Java
import java.io.*;
import java.util.*;
class GFG{
static int Octadecagonal_num( int n)
{
return ( 16 * n * n - 14 * n) / 2 ;
}
public static void main(String[] args)
{
int n = 3 ;
System.out.println(Octadecagonal_num(n));
n = 10 ;
System.out.println(Octadecagonal_num(n));
}
}
|
Python3
def Octadecagonal_num(n):
return ( 16 * n * n - 14 * n) / 2
n = 3
print ( int (Octadecagonal_num(n)))
n = 10
print ( int (Octadecagonal_num(n)))
|
C#
using System;
class GFG{
static int Octadecagonal_num( int n)
{
return (16 * n * n - 14 * n) / 2;
}
public static void Main( string [] args)
{
int n = 3;
Console.Write(Octadecagonal_num(n) + "\n" );
n = 10;
Console.Write(Octadecagonal_num(n) + "\n" );
}
}
|
Javascript
<script>
function Octadecagonal_num(n)
{
return (16 * n * n - 14 * n) / 2;
}
let n = 3;
document.write(Octadecagonal_num(n) + "</br>" );
n = 10;
document.write(Octadecagonal_num(n));
</script>
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Reference: https://en.wikipedia.org/wiki/Polygonal_number
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