求系列 4、11、30、85、248 的第 N 项。 .

给定一个正整数N 。任务是找到系列的第 N项：

4, 11, 30, 85, 248…

例子：

Input: N = 4
Output: 85

Input: N = 2
Output: 11

方法：

给定序列的第 N 项可以概括为：

T_N = 3^N + N

插图：

Input: N = 4
Output: 85
Explanation: 
T_N = 3^N +N
     = 3⁴ + 4
     = 81 +4
     = 85

下面是上述问题的实现：

C++

// C++ program to find N-th term
// of the series-
// 4, 11, 30, 85, 248...
#include 
using namespace std;
 
// Function to return Nth term
// of the series
int nthTerm(int N)
{
    return pow(3, N) + N;
}
 
// Driver Code
int main()
{
    // Get the value of N
    int N = 4;
    cout << nthTerm(N);
    return 0;
}

Java

// Java program to find N-th term
// of the series-
// 4, 11, 30, 85, 248...
class GFG
{
 
  // Function to return Nth term
  // of the series
  static int nthTerm(int N) {
    return (int)Math.pow(3, N) + N;
  }
 
  // Driver Code
  public static void main(String args[])
  {
 
    // Get the value of N
    int N = 4;
    System.out.println(nthTerm(N));
  }
}
 
// This code is contributed by saurabh_jaiswal.

Python3

# Python code for the above approach
 
# Function to return Nth term
# of the series
def nthTerm(N):
    return (3 ** N) + N;
 
# Driver Code
# Get the value of N
N = 4;
print(nthTerm(N));
 
# This code is contributed by Saurabh Jaiswal

C#

// C# program to find N-th term
// of the series-
// 4, 11, 30, 85, 248...
using System;
class GFG
{
 
  // Function to return Nth term
  // of the series
  static int nthTerm(int N) {
    return (int)Math.Pow(3, N) + N;
  }
 
  // Driver Code
  public static void Main()
  {
 
    // Get the value of N
    int N = 4;
    Console.Write(nthTerm(N));
  }
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript

      // JavaScript code for the above approach
 
      // Function to return Nth term
      // of the series
      function nthTerm(N) {
          return Math.pow(3, N) + N;
      }
 
      // Driver Code
 
      // Get the value of N
      let N = 4;
      document.write(nthTerm(N));
 
// This code is contributed by Potta Lokesh
  

输出

85

时间复杂度： O(1)

辅助空间： O(1)