二十面体编号

给定数字n，找到第n个二十面体数。二十面体数是表示二十面体(具有20个面的多面体)的比喻数字类。来源：Wiki。

前几个二十面体编号是1、12、48、124、255、456、742、1128、1629…………..

例子 ：

Input : 5
Output :255

Input :10
Output :2260

二十面体数的第n个项由下式给出：

$I_{n}=\frac{n(5n^2-5n+2)}{2}$

以上思想基本实现：

C++

// Icosahedral number to find
// n-th term in C++
#include 
using namespace std;
  
// Function to find
// Icosahedral number
int icosahedralnum(int n)
{
    // Formula to calculate nth
    // Icosahedral number &
    // return it into main function.
    return (n * (5 * n * n - 5 * n + 2)) / 2;
}
  
// Driver Code
int main()
{
    int n = 7;
  
    cout << icosahedralnum(n);
    return 0;
}

Java

// Icosahedral number to find
// n-th term in Java
import java.io.*;
  
class GFG {
      
    // Function to find
    // Icosahedral number
    static int icosahedralnum(int n)
    {
        // Formula to calculate nth
        // Icosahedral number &
        // return it into main function.
          
        return (n * (5 * n * n - 5 *
                            n + 2)) / 2;
    }
  
    // Driver Code
    public static void main (String[] args) 
    {
        int n = 7;
        System.out.println(
                        icosahedralnum(n));
    }
}
  
// This code is contributed by aj_36.

Python3

# Python 3 Program to find 
# nth Icosahedral number
  
# Icosahedral number
# number function
def icosahedralnum(n) :
      
    # Formula to calculate nth
    # Icosahedral number
    # return it into main function.
    return (n * (5 * n * n - 
                 5 * n + 2)) // 2
  
  
# Driver Code
if __name__ == '__main__' :
          
    n = 7
    print(icosahedralnum(n))
  
# This code is contributed aj_36

C#

// Icosahedral number to 
// find n-th term in C#
using System;
  
class GFG
{
      
    // Function to find
    // Icosahedral number
    static int icosahedralnum(int n)
    {
        // Formula to calculate
        // nth Icosahedral number
        // & return it into main 
        // function.
        return (n * (5 * n * n - 
                     5 * n + 2)) / 2;
    }
  
    // Driver Code
    static public void Main ()
    {
        int n = 7;
        Console.WriteLine(icosahedralnum(n));
    }
}
  
// This code is contributed by ajit

输出

742