número heptagonal

Dado un número n, la tarea es encontrar el N-ésimo número heptagonal. Un número heptagonal representa un heptágono y pertenece a un número figurativo. Heptagonal tiene siete ángulos, siete vértices y un polígono de siete lados. 
Ejemplos:
 

Entrada: 2 
Salida: 7
Entrada: 15 
Salida: 540 
 

Pocos números heptagonales son: 
1, 7, 18, 34, 55, 81, 112, 148, 189, 235………..
Una fórmula para calcular el N-ésimo número heptagonal: 
 

// 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 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 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.

# 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# 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 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.
?>

<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>

7
540

Complejidad Temporal: O(1), ya que no hay bucle ni recursividad.
Espacio Auxiliar: O(1), ya que no se ha ocupado ningún espacio extra.
Referencia: https://en.wikipedia.org/wiki/Heptagonal_number