程序找到系列-1、2、11、26、47的第N个项……

给定数字N，任务是找到该系列的第N个项：

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

例子：

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

方法：
给定级数的N个项可以概括为：

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

下面是上述问题的实现：
程序：

C++

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

Javascript

 
// 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
 

输出：

11

时间复杂度： O(1)