中心十角数

给定一个数 n，找出第n 个中心十边形数 。
中心十边形数是居中的图形数，它代表一个以点为中心的十边形和以连续十边形形式围绕它的所有其他点。来源[维基]。

前几个中心十边形数是：
1、11、31、61、101、151、211、281、361、451、551、661…………
例子 ：

Input :  3
Output : 31

Input : 6
Output : 151

在数学中，第 n项的以数学为中心的十边形数由下式给出：

$Cd_{n}= 5n^2+5n+1$

下面是上述想法的基本实现。

C++

// Program to find nth
// centered decagonal
// number
#include 
using namespace std;
 
// Centered decagonal
// number function
 
int centereddecagonalnum(int n)
{
    // Formula to calculate nth
    // centered decagonal number &
    // return it into main function.
    return (5 * n * n + 5 * n + 1);
}
 
// Driver Code
int main()
{
    int n = 5;
    cout << n << "th centered decagonal"
                          << "number: ";
    cout << centereddecagonalnum(n);
    cout << endl;
    n = 9;
    cout << n << "th centered decagonal"
                          << "number: ";
    cout << centereddecagonalnum(n);
 
    return 0;
}

Java

// Java Program to find nth
// centered decagonal number
import java.io.*;
 
class GFG
{
     
    // Centered decagonal
    // number function
    static int centereddecagonalnum(int n)
    {
         
    // Formula to calculate nth
    // centered decagonal number &
    // return it into main function.
    return (5 * n * n + 5 * n + 1);
    }
 
    // Driver Code
    public static void main (String[] args)
    {
        int n = 5;
        System.out.print(n + "th centered " +
                       "decagonal number: ");
        System.out.println(centereddecagonalnum(n));
 
        n = 9;
        System.out.print(n + "th centered " +
                       "decagonal number: ");
        System.out.println(centereddecagonalnum(n));
    }
}
 
// This code is contributed by m_kit

Python3

# Program to find nth
# centered decagonal number
 
# Centered decagonal
# number function
def centereddecagonalnum(n) :
     
    # Formula to calculate
    # nth centered decagonal
    # number & return it
    # into main function.
    return (5 * n * n +
            5 * n + 1)
 
# Driver Code
if __name__ == '__main__' :
         
    n = 5
    print(n,"th centered decagonal " +
                          "number : ",
              centereddecagonalnum(n))
 
    n = 9
    print(n,"th centered decagonal " +
                          "number : ",
              centereddecagonalnum(n))
               
# This code is contributed by m_kit

C#

// Program to find nth
// centered decagonal
// number
using System;
 
class GFG
{
// Centered decagonal
// number function
static int centereddecagonalnum(int n)
{
    // Formula to calculate nth
    // centered decagonal number &
    // return it into main function.
    return (5 * n * n + 5 * n + 1);
}
 
// Driver Code
static public void Main ()
{
int n = 5;
Console.Write(n + "th centered decagonal"+
                              "number: ");
Console.WriteLine(centereddecagonalnum(n));
 
n = 9;
Console.Write(n + "th centered decagonal"+
                              "number: ");
Console.WriteLine(centereddecagonalnum(n));
}
}
 
// This code is contributed by aj_36

Javascript

 
// Javascript Program to find nth
// centered decagonal number
 
// Centered decagonal
// number function
function centereddecagonalnum(n)
{
     
    // Formula to calculate nth
    // centered decagonal number &
    // return it into main function.
    return (5 * n * n + 5 * n + 1);
}
 
// Driver Code
var n = 5;
document.write(n + "th centered " +
               "decagonal number: ");
document.write(centereddecagonalnum(n) + "<br>");
 
n = 9;
document.write(n + "th centered " +
               "decagonal number: ");
document.write(centereddecagonalnum(n));
 
// This code is contributed by Kirti
     

输出

5th centered decagonalnumber: 151
9th centered decagonalnumber: 451

时间复杂度： O(1)
辅助空间： O(1)

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