# Octacontagon Number

Last Updated : 07 Oct, 2021

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

A Octacontagon number is class of figurate number. It has 80 – sided polygon called octacontagon. The N-th octacontagon number countâ€™s the 80 number of dots and all others dots are surrounding with a common sharing corner and make a pattern. The first few octacontagonol numbers are 1, 80, 237, 472 …

Examples:

Input: N = 2
Output: 80
Explanation:
The second octacontagonol number is 80.

Input: N = 3
Output: 237

Approach: The N-th octacontagon number is given by the formula:

• Nth term of s sided polygon =
• Therefore Nth term of 80 sided polygon is

Below is the implementation of the above approach:

## C++

 // C++ program for above approach#include using namespace std; // Finding the nth octacontagon Numberint octacontagonNum(int n){    return (78 * n * n - 76 * n) / 2;} // Driver Codeint main(){    int n = 3;    cout <<"3rd octacontagon Number is = "         << octacontagonNum(n);     return 0;} // This code is contributed by shivanisinghss2110

## C

 // C program for above approach#include #include  // Finding the nth octacontagon Numberint octacontagonNum(int n){    return (78 * n * n - 76 * n) / 2;} // Driver program to test above functionint main(){    int n = 3;    printf("3rd octacontagon Number is = %d",           octacontagonNum(n));     return 0;}

## Java

 // Java program for above approachimport java.util.*;class GFG{ // Finding the nth octacontagon Numberstatic int octacontagonNum(int n){    return (78 * n * n - 76 * n) / 2;} // Driver Codepublic static void main(String args[]){    int n = 3;    System.out.print("3rd octacontagon Number is = " +                                  octacontagonNum(n));}} // This code is contributed by Akanksha_Rai

## Python3

 # Python3 program for above approach  # Finding the nth octacontagon number def octacontagonNum(n):      return (78 * n * n - 76 * n) // 2 # Driver coden = 3print("3rd octacontagon Number is = ",                    octacontagonNum(n))  # This code is contributed by divyamohan123

## C#

 // C# program for above approachusing System;class GFG{ // Finding the nth octacontagon Numberstatic int octacontagonNum(int n){    return (78 * n * n - 76 * n) / 2;} // Driver Codepublic static void Main(){    int n = 3;    Console.Write("3rd octacontagon Number is = " +                               octacontagonNum(n));}} // This code is contributed by Akanksha_Rai

## Javascript

 

Output:
3rd octacontagon Number is = 237

Time Complexity: O(1)

Auxiliary Space: O(1)