求系列 3、5、9、17、33 的第 N 项。 .

给定一个正整数N ，任务是找到序列的第 N项-

3, 5, 9, 17, 33…till N terms

例子：

Input: N = 4
Output: 17

Input: N = 3
Output: 9

方法：

考虑下面的例子：

Lets say N = 4

The 4th term of the given series is 17, i.e. : 2 ^ 4 + 1 = 16 + 1 = 17

Similarly, lets say N = 3

The 3rd term of the given series is : 2 ^ 3 + 1 = 8 + 1 = 9 (which is correct).

因此，我们可以使用上述观察来找出序列的第 N项的关系：

1st term = 3 = 2¹ + 1

2nd term = 2² + 1 = 5

3rd term = 2³ + 1 = 9

4th term = 2⁴ + 1 = 17

.

.

Therefore, Nth term can be found out using following relation: 2^N + 1

Upon generalising, the relation for Nth term can be represented as:

$T_{N} = 2^{N} + 1$

以下是上述方法的实现 -

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Function to return Nth
// term of the series
int findTerm(int N)
{
    return pow(2, N) + 1;
}
 
// Driver Code
int main()
{
    int N = 6;
    cout << findTerm(N);
    return 0;
}

Java

// Java program to implement
// the above approach
import java.io.*;
 
class GFG {
 
  // Function to return Nth
  // term of the series
  static int findTerm(int N)
  {
    return (int)Math.pow(2, N) + 1;
  }
 
  // Driver Code
  public static void main (String[] args)
  {
    int N = 6;
    System.out.print(findTerm(N));
  }
}
 
// This code is contributed by Shubham Singh

Python3

# Python program to implement
# the above approach
 
# Function to return Nth
# term of the series
def findTerm(N):
    return (2 ** N) + 1;
 
# Driver Code
N = 6;
print(findTerm(N));
 
# This code is contributed by gfgking

C#

// C# program to implement
// the above approach
using System;
class GFG
{
 
  // Function to return Nth
  // term of the series
  static int findTerm(int N)
  {
    return (int)Math.Pow(2, N) + 1;
  }
 
  // Driver Code
  public static void Main()
  {
    int N = 6;
    Console.Write(findTerm(N));
  }
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript

    // JavaScript program to implement
    // the above approach
 
    // Function to return Nth
    // term of the series
    const findTerm = (N) => {
        return Math.pow(2, N) + 1;
    }
 
    // Driver Code
    let N = 6;
    document.write(findTerm(N));
 
// This code is contributed by rakeshsahni
 

输出

65

时间复杂度： O(1)
辅助空间： O(1)