十六进制数

给定一个数 n，任务是找到第 n 个 Hendecagonal 数。
Hendecagonal number 是一个图形数字，它将三角形和正方形数字的概念扩展到十边形（11 边多边形）。第 n 个十边形数计算 n 个嵌套十边形图案中的点数，所有十边形都共享一个公共角，其中图案中的第 i 个十边形的边由 i 个点组成，彼此间隔一个单位。
例子：

Input : 2 
Output :11
Input :6 
Output :141 
 

第 n 个十边形数的公式：

$\begin{math} H_{n}=((9n^2)-7n)/2 \end{math}$

C++

// C++ program to find nth
// Hendecagonal number
#include 
using namespace std;
 
// Function to find
// Hendecagonal number
int hendecagonal_num(int n)
{
    // Formula to calculate nth
    // Hendecagonal number
    return (9 * n * n - 7 * n) / 2;
}
 
// Driver Code
int main()
{
    int n = 3;
    cout << n << "rd Hendecagonal number: ";
    cout << hendecagonal_num(n);
    cout << endl;
    n = 10;
    cout << n << "th Hendecagonal number: ";
    cout << hendecagonal_num(n);
 
    return 0;
}

Java

// Java program to find nth
// Hendecagonal number
import java.io.*;
 
class GFG
{
     
// Function to find
// Hendecagonal number
static int hendecagonal_num(int n)
{
    // Formula to calculate nth
    // Hendecagonal number
    return (9 * n * n -
            7 * n) / 2;
}
 
// Driver Code
public static void main (String[] args)
{
int n = 3;
System.out.print(n + "rd Hendecagonal " +
                             "number: ");
System.out.println(hendecagonal_num(n));
 
n = 10;
System.out.print(n + "th Hendecagonal " +
                             "number: ");
System.out.println(hendecagonal_num(n));
}
}
 
// This code is contributed by ajit

Python3

# Program to find nth
# Hendecagonal number
 
# Function of Hendecagonal
# number
def hendecagonal_num(n) :
     
    # Formula to calculate nth
    # Hendecagonal number &
    # return it into main function.
     
    return (9 * n * n -
            7 * n) // 2
 
# Driver Code
if __name__ == '__main__' :
         
    n = 3
    print(n,"rd Hendecagonal number : " ,
                    hendecagonal_num(n))
 
    n = 10
    print(n,"th Hendecagonal number : " ,
                    hendecagonal_num(n))
 
# This code is contributed by ajit

C#

// C# program to find nth
// Hendecagonal number
using System;
 
class GFG
{
// Function to find
// Hendecagonal number
static int hendecagonal_num(int n)
{
    // Formula to calculate nth
    // Hendecagonal number
    return (9 * n * n - 7 * n) / 2;
}
 
// Driver Code
static public void Main ()
{
    int n = 3;
    Console.Write(n +
                 "rd Hendecagonal number: ");
    Console.WriteLine( hendecagonal_num(n));
 
    n = 10;
    Console.Write(n +
                 "th Hendecagonal number: ");
    Console.WriteLine( hendecagonal_num(n));
    }
}
 
// This code is contributed by aj_36

Javascript

    // Javascript program to find nth
    // Hendecagonal number
     
    // Function to find
    // Hendecagonal number
    function hendecagonal_num(n)
    {
        // Formula to calculate nth
        // Hendecagonal number
        return (9 * n * n - 7 * n) / 2;
    }
     
    let n = 3;
    document.write(n + "rd Hendecagonal number: ");
    document.write(hendecagonal_num(n) + "</br>");
    n = 10;
    document.write(n + "th Hendecagonal number: ");
    document.write(hendecagonal_num(n));
 
// This code is contributed by divyesh072019.

输出 ：

3th Hendecagonal number: 30
10th Hendecagonal number: 415

时间复杂度： O(1)
辅助空间： O(1)

参考：https://en.wikipedia.org/wiki/Polygonal_number