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# Icosagonal number

• Last Updated : 16 Jul, 2021

Given a number n, the task is to find the nth Icosagonal number.
An Icosagonal number is the 20-gon is a twenty-sided polygon. The number derived from the figurative class. There are different pattern series number in this number. The dots are countable, arrange in a specific way of position and create a diagram. All the dots have a common dots points, all others dots are connected to this points and except this common point the dots connected to their i-th dots with their respective successive layer.
Examples :

Input : 3
Output :57
Input :8
Output :512

Formula for nth icosagonal number:

## C++

 // C++ program to find// nth Icosagonal number#include using namespace std; // Function to calculate Icosagonal numberint icosagonal_poly(long int n){    // Formula for finding    // nth Icosagonal number    return (18 * n * n - 16 * n) / 2;} // Drivers codeint main(){    long int n = 7;    cout << n << "th Icosagonal number :"               << icosagonal_poly(n);     return 0;}

## Java

 // Java program to find// nth Icosagonal number import java.io.*; class GFG {     // Function to calculate Icosagonal number static int icosagonal_poly(int n){    // Formula for finding    // nth Icosagonal number    return (18 * n * n - 16 * n) / 2;} // Drivers code         public static void main (String[] args) {        int n = 7;         System.out.print (n + "th Icosagonal number :");    System.out.println(icosagonal_poly(n));    }}// This code is contributed by aj_36

## Python 3

 # Python 3 program to find# nth Icosagonal number # Function to calculate# Icosagonal numberdef icosagonal_poly(n) :         # Formula for finding    # nth Icosagonal number    return (18 * n * n -            16 * n) // 2 # Driver Codeif __name__ == '__main__' :    n = 7    print(n,"th Icosagonal number : ",                   icosagonal_poly(n)) # This code is contributed m_kit

## C#

 // C# program to find// nth Icosagonal numberusing System; class GFG{ // Function to calculate// Icosagonal numberstatic int icosagonal_poly(int n){    // Formula for finding    // nth Icosagonal number    return (18 * n * n -            16 * n) / 2;} // Driver codestatic public void Main (){     int n = 7; Console.Write(n + "th Icosagonal " +                        "number :");Console.WriteLine(icosagonal_poly(n));}} // This code is contributed by ajit

## PHP

 

## Javascript

 

Output :

7th Icosagonal number :385

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

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