Icosagonal number

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 <bits/stdc++.h>
using namespace std;

// Function to calculate Icosagonal number
int icosagonal_poly(long int n)
{
    // Formula for finding
    // nth Icosagonal number
    return (18 * n * n - 16 * n) / 2;
}

// Drivers code
int main()
{
    long int n = 7;
    cout << n << "th Icosagonal number :"
               << icosagonal_poly(n);

    return 0;
}

C

// C program to find
// nth Icosagonal number
#include <stdio.h>

// Function to calculate Icosagonal number
int icosagonal_poly(long int n)
{

    // Formula for finding
    // nth Icosagonal number
    return (18 * n * n - 16 * n) / 2;
}

// Drivers code
int main()
{
    long int n = 7;
    printf("%ldth Icosagonal number : %d",n,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 number
def icosagonal_poly(n) :

    # Formula for finding
    # nth Icosagonal number
    return (18 * n * n -
            16 * n) // 2

# Driver Code
if __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 number
using System;

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;
}

// Driver code
static public void Main ()
{

int n = 7;

Console.Write(n + "th Icosagonal " +
                        "number :");
Console.WriteLine(icosagonal_poly(n));
}
}

// This code is contributed by ajit

PHP

<?php
// PHP program to find
// nth Icosagonal number

// Function to calculate
// Icosagonal number
function icosagonal_poly($n)
{
    // Formula for finding
    // nth Icosagonal number
    return (18 * $n *
            $n - 16 * $n) / 2;
}

// Driver Code
$n = 7;
echo $n , "th Icosagonal number :",
               icosagonal_poly($n);

// This code is contributed by ajit
?>

Javascript

<script>
    // Javascript program to find nth Icosagonal number

    // Function to calculate
    // Icosagonal number
    function icosagonal_poly(n)
    {
        // Formula for finding
        // nth Icosagonal number
        return (18 * n * n - 16 * n) / 2;
    }

    let n = 7;

    document.write(n + "th Icosagonal number :");
    document.write(icosagonal_poly(n));

</script>

Output :

7th Icosagonal number :385

Time Complexity: O(1)
Auxiliary Space: O(1)
Reference: https://en.wikipedia.org/wiki/Polygonal_number