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Second decagonal numbers
  • Last Updated : 06 Apr, 2021

The Second decagonal numbers series can be represented as 

7, 22, 45, 76, 115, 162, 217, 280,,…..

Nth term
Given an integer N. The task is to find the N-th term of the given series.
Examples

Input: N = 1 
Output: 7

Input: N = 4 
Output: 76   



Approach: The idea is to find the general term for the Second decagonal numbers. Below is the computation of the general term for second decagonal numbers:  

1st Term = 1 * (4*1 + 3) = 7 
2nd term = 2 * (4*2 + 3) = 22 
3rd term = 3 * (4*3 + 3) = 45 
4th term = 4 * (4*4 + 3) = 76 



Nth term = n * (4 * n + 3) 
Therefore, the Nth term of the series is given as N * (4 * N + 3)

Below is the implementation of above approach: 

C++




// C++ implementation to
// find N-th term in the series
 
#include <iostream>
#include <math.h>
using namespace std;
 
// Function to find N-th term
// in the series
void findNthTerm(int n)
{
    cout << n * (4 * n + 3) << endl;
}
 
// Driver Code
int main()
{
    int N = 4;
    findNthTerm(N);
 
    return 0;
}

Java




// Java program for the above approach
class GFG{
 
// Function to find N-th term
// in the series
static void findNthTerm(int n)
{
    System.out.println(n * (4 * n + 3));
}
 
// Driver code
public static void main(String[] args)
{
    int N = 4;
     
    findNthTerm(N);
}
}
 
// This code is contributed by Pratima Pandey

Python3




# Python3 implementation to
# find N-th term in the series
 
# Function to find N-th term
# in the series
def findNthTerm(n):
 
    print(n * (4 * n + 3))
 
# Driver Code
N = 4;
findNthTerm(N);
 
# This code is contributed by Code_Mech

C#




// C# program for the above approach
using System;
class GFG{
 
// Function to find N-th term
// in the series
static void findNthTerm(int n)
{
    Console.WriteLine(n * (4 * n + 3));
}
 
// Driver code
public static void Main(String[] args)
{
    int N = 4;
     
    findNthTerm(N);
}
}
 
// This code is contributed by 29AjayKumar

Javascript




<script>
// Javascript implementation to
// find N-th term in the series
 
// Function to find N-th term
// in the series
function findNthTerm(n)
{
    document.write(n * (4 * n + 3));
}
 
// Driver Code
let N = 4;
findNthTerm(N);
 
// This code is contributed by subhammahato348.
</script>
Output: 
76

 

Time Complexity: O(1)

Auxiliary Space: O(1)

Reference: OEIS

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