Heptagonal number

Given a number n, the task is to find Nth heptagonal number. A Heptagonal number represents heptagon and belongs to a figurative number. Heptagonal has seven angles, seven vertices, and seven-sided polygon. 
Examples :

Input : 2 
Output :7
Input :15 
Output :540 

Few Heptagonal numbers are : 
1, 7, 18, 34, 55, 81, 112, 148, 189, 235………..
A formula to calculate Nth Heptagonal number: 

C++

// C++ program to find the
// nth Heptagonal number
#include <iostream>
using namespace std;

// Function to return Nth Heptagonal
// number
int heptagonalNumber(int n)
{
    return ((5 * n * n) - (3 * n)) / 2;
}

// Drivers Code
int main()
{

    int n = 2;
    cout << heptagonalNumber(n) << endl;
    n = 15;
    cout << heptagonalNumber(n) << endl;

    return 0;
}

C

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

// Function to return Nth Heptagonal
// number
int heptagonalNumber(int n)
{
  return ((5 * n * n) - (3 * n)) / 2;
}

// Drivers Code
int main()
{

  int n = 2;
  printf("%d\n",heptagonalNumber(n));

  n = 15;
  printf("%d\n",heptagonalNumber(n));

  return 0;
}

// This code is contributed by kothavvsaakash.

Java

// Java program to find the
// nth Heptagonal number
import java.io.*;

class GFG
{
// Function to return
// Nth Heptagonal number
static int heptagonalNumber(int n)
{
    return ((5 * n * n) - (3 * n)) / 2;
}

// Driver Code
public static void main (String[] args)
{
    int n = 2;
    System.out.println(heptagonalNumber(n));
    n = 15;
    System.out.println(heptagonalNumber(n));
}
}

// This code is contributed by anuj_67.

Python3

# Program to find nth
# Heptagonal number

# Function to find
# nth Heptagonal number
def heptagonalNumber(n) :

    # Formula to calculate
    # nth Heptagonal number
    return ((5 * n * n) -
            (3 * n)) // 2

# Driver Code
if __name__ == '__main__' :
    n = 2
    print(heptagonalNumber(n))
    n = 15
    print(heptagonalNumber(n))

# This code is contributed
# by ajit

C#

// C# program to find the
// nth Heptagonal number
using System;

class GFG
{
// Function to return
// Nth Heptagonal number
static int heptagonalNumber(int n)
{
    return ((5 * n * n) -
            (3 * n)) / 2;
}

// Driver Code
public static void Main ()
{
    int n = 2;
    Console.WriteLine(heptagonalNumber(n));
    n = 15;
    Console.WriteLine(heptagonalNumber(n));
}
}

// This code is contributed by anuj_67.

PHP

<?php
// PHP program to find the
// nth Heptagonal number

// Function to return Nth
// Heptagonal number
function heptagonalNumber($n)
{
    return ((5 * $n * $n) -
            (3 * $n)) / 2;
}

// Driver Code
$n = 2;
echo heptagonalNumber($n), "\n";
$n = 15;
echo heptagonalNumber($n);

// This code is contributed
// by anuj_67.
?>

Javascript

<script>
// Javascript program to find the
// nth Heptagonal number

// Function to return Nth Heptagonal
// number
function heptagonalNumber(n)
{
    return parseInt(((5 * n * n) - (3 * n)) / 2);
}

// Drivers Code
let n = 2;
document.write(heptagonalNumber(n) + "<br>");
n = 15;
document.write(heptagonalNumber(n) + "<br>");

// This code is contributed by rishavmahato348.
</script>

Output :

7
540

Time Complexity: O(1), since there is no loop or recursion.
Auxiliary Space: O(1), since no extra space has been taken.
Reference: https://en.wikipedia.org/wiki/Heptagonal_number