Program to find the Nth term of series -1, 2, 11, 26, 47……

Given a number N, the task is to find the Nth term of this series: 

-1, 2, 11, 26, 47, 74, .....

Examples:

Input: 3
Output: 11
Explanation:
when N = 3
Nth term = ( (3 * N * N) - (6 * N) + 2 )
         = ( (3 * 3 * 3) - (6 * 3) + 2 )
         = 11

Input: 9
Output: 191

Approach:
The Nth term of the given series can be generalised as: 

Nth term of the series : ( (3 * N * N) - (6 * N) + 2 )

Below is the implementation of the above problem:
Program:

C++

// CPP program to find N-th term of the series:
// 9, 23, 45, 75, 113, 159......

#include <iostream>;
using namespace std;
// calculate Nth term of series
int nthTerm(int N)
{
    return ((3 * N * N) - (6 * N) + 2);
}

// Driver Function
int main()
{

    // Get the value of N
    int N = 3;

    // Find the Nth term
    // and print it
    cout << nthTerm(N);

    return 0;
}

Java

// Java program to find N-th term of the series:
// 9, 23, 45, 75, 113, 159......
 class GFG {

    // calculate Nth term of series
    static int nthTerm(int N)
    {
        return ((3 * N * N) - (6 * N) + 2);
    }

    // Driver code
    public static void main(String[] args) {
        int N = 3;

        // Find the Nth term
        // and print it
        System.out.println(nthTerm(N));
    }
}

// This code is contributed by bilal-hungund

Python3

# Python3 program to find N-th term
# of the series:
# 9, 23, 45, 75, 113, 159......

def nthTerm(N):

    #calculate Nth term of series
    return ((3 * N * N) - (6 * N) + 2);

# Driver Code
if __name__=='__main__':
    n = 3

    #Find the Nth term
    # and print it
    print(nthTerm(n))

# this code is contributed by bilal-hungund

C#

// C# program to find N-th term of the series:
// 9, 23, 45, 75, 113, 159......
using System;
class GFG
{

// calculate Nth term of series
static int nthTerm(int N)
{
    return ((3 * N * N) - (6 * N) + 2);
}

// Driver code
public static void Main()
{
    int N = 3;

    // Find the Nth term
    // and print it
    Console.WriteLine(nthTerm(N));
}
}

// This code is contributed by inder_verma

PHP

<?php
// PHP program to find N-th term of
// the series: 9, 23, 45, 75, 113, 159......

// calculate Nth term of series
function nthTerm($N)
{
    return ((3 * $N * $N) -
            (6 * $N) + 2);
}

// Driver Code

// Get the value of N
$N = 3;

// Find the Nth term
// and print it
echo nthTerm($N);

// This code is contributed by Raj
?>

Javascript

<script>

// JavaScript program to find N-th term of the series:
// 9, 23, 45, 75, 113, 159......


    // calculate Nth term of series
    function nthTerm(N)
    {
        return ((3 * N * N) - (6 * N) + 2);
    }

    // Driver Function

    // Get the value of N
    let N = 3;

    // Find the Nth term
    // and print it
    document.write(nthTerm(N));

// This code is contributed by Surbhi Tyagi

</script>

Output:

11

Time Complexity: O(1)

Space Complexity: O(1) since using constant variables