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Decagonal Numbers
  • Last Updated : 09 Apr, 2021

You are given a number n, the task is to find the nth Decagonal number. A decagonal number is a figurate number that extends the concept of triangular and square numbers to the decagon (a ten-sided polygon). The nth decagonal numbers counts the number of dots in a pattern of n nested decagons, all sharing a common corner, where the ith decagon in the pattern has sides made of i dots spaced one unit apart from each other.

Examples: 

Input : n = 3
Output : 27

Input : n = 7
Output : 175
 
 

The n-th decagonal number is given by the formula 
(4n 2 – 3n)

C++




// C++ program to find nth decagonal number
#include <bits/stdc++.h>
using namespace std;
  
// Function to calculate decagonal number
int decagonal(int n)
{
    // Formula for finding nth decagonal number
    return 4 * n * n - 3 * n;
}
  
// Driver function
int main()
{
    int n = 10;
    cout << n << "th decagonal number :" << decagonal(n);
    return 0;
}

Java




// JAVA Code for Decagonal Numbers
import java.util.*;
 
class GFG {
 
    // Function to calculate
    // decagonal number
    static int decagonal(int n)
    {
        // Formula for finding nth
        // decagonal number
        return 4 * n * n - 3 * n;
    }
     
    /* Driver function */
    public static void main(String[] args)
    {   
        int n = 10;
        System.out.println(n + "th decagonal number :"
                            + decagonal(n));
    }
}
 
// This code is contributed by Arnav Kr. Mandal.

Python




# Python program to find nth decagonal number
def decagonal(n):
    return 4 * n * n - 3 * n
  
# Driver code
n = 10
print(n, "th decagonal number :", decagonal(n))

C#




// C# Code for Decagonal Numbers
using System;
 
class GFG {
 
    // Function to calculate
    // decagonal number
    static int decagonal(int n)
    {
        // Formula for finding nth
        // decagonal number
        return 4 * n * n - 3 * n;
    }
     
    // Driver Code
    public static void Main()
    {
        int n = 10;
        Console.Write(n + "th decagonal number : "
                                   + decagonal(n));
    }
}
 
// This code is contributed by vt_m.

PHP




<?php
// PHP program to find nth
// decagonal number
 
// Function to calculate
// decagonal number
function decagonal($n)
{
     
    // Formula for finding nth
    // decagonal number
    return 4 * $n * $n - 3 * $n;
}
 
// Driver function
$n = 10;
echo $n, "th decagonal number :",
                 decagonal($n);
 
// This code is contributed by ajit
?>

Javascript




<script>
 
// JavaScript program for Decagonal Numbers
 
// Function to calculate
// decagonal number
function decagonal(n)
{
     
    // Formula for finding nth
    // decagonal number
    return 4 * n * n - 3 * n;
}
 
// Driver code
let n = 10;
document.write(n + "th decagonal number : " +
               decagonal(n));
                
// This code is contributed by souravghosh0416
 
</script>

Output: 

10th decagonal number : 370

 

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