八面体数

给定数字n，任务是找到第n个八面体数。
八面体数属于伪造数，它是由紧密堆积的球体构成的八面体中的球体数。前几个八面体数(其中n = 0、1、2、3…。)是：0、1、6、19，依此类推。
例子 ：

Input : 4 
Output : 44
Input : 8 
Output : 344 
 

第n个八面体数的公式：

n * (2n2+1) / 3

C++

// C++ program to find nth
// octahedral number
#include 
using namespace std;
 
// Function to find
// octahedral number
int octahedral_num(int n)
{
    // Formula to calculate nth
    // octahedral number
    return n * (2 * n * n + 1) / 3;
}
 
// Drivers code
int main()
{
    int n = 5;
 
    // print result
    cout << n << "th Octahedral number: ";
    cout << octahedral_num(n);
    return 0;
}

Java

// Java program to find nth octahedral
// number
import java.io.*;
 
class GFG {
 
    // Function to find octahedral number
    static int octahedral_num(int n)
    {
 
        // Formula to calculate nth
        // octahedral number
        // and return it into main function.
        return n * (2 * n * n + 1) / 3;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        int n = 5;
        // print result
        System.out.print(n + "th Octahedral"
                         + " number: ");
        System.out.println(octahedral_num(n));
    }
}

Python3

# Python 3 program to find nth
# octahedral number
 
# Function to find
# octahedral number
def octahedral_num(n) :
     
    # Formula to calculate nth
    # octahedral number
    return n * (2 * n * n + 1) // 3
 
# Driver Code
if __name__ == '__main__' :
         
    n = 5
    print(n,"th Octahedral number: "
                , octahedral_num(n))
 
# This code is contributed ajit.

C#

// C# program to find nth
// Octahedral number
using System;
 
class GFG
{
     
    // Function to find
    // octahedral number
    static int octahedral_num(int n)
    {
 
        // Formula to calculate
        // nth octahedral number
        // and return it into
        // main function.
        return n * (2 * n *
                    n + 1) / 3;
    }
 
    // Driver Code
    static public void Main ()
    {
        int n = 5;
         
        // print result
        Console.Write(n + "th Octahedral"
                        + " number: ");
        Console.WriteLine(octahedral_num(n));
    }
}
 
// This code is Contributed by m_kit

Javascript

 
// JavaScript program to find nth
// octahedral number
 
 
// Function to find
// octahedral number
function octahedral_num( n)
{
    // Formula to calculate nth
    // octahedral number
    // and return it into main function.
    return n * (2 * n * n + 1) / 3;
}
 
// Drivers Code
let n = 5;
 
// print result
document.write( n+ "th Octahedral number: ");
document.write(octahedral_num(n));
 
// This code is contributed by Bobby
 

输出 ：

5th Octahedral number: 85

参考：https：//en.wikipedia.org/wiki/八面体编号