求系列 12, 14, 24, 58, 164, ... 的 N 项之和

给定一个正整数N 。求系列12, 14, 24, 58, 164, ....的前N 项之和

例子：

Input: N = 5
Output: 272

Input: N = 3
Output: 50

方法：

该序列是通过使用以下模式形成的。对于任何值 N-

S_N = 3^N – N² + 11 * N – 1

插图：

Input: N = 5
Output: 272
Explanation:
S_N = 3^N – N² + 11 * N – 1
     = 3⁵ – 5² + 11 * 5 – 1
     = 243 – 25 + 54
     = 272

下面是上述方法的实现：

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Function to return sum of
// N term of the series
int findSum(int N)
{
    return (pow(3, N) -
            pow(N, 2) +
            11 * N - 1);
}
 
// Driver Code
int main()
{
    int N = 5;
    cout << findSum(N);
    return 0;
}

Java

// Java program to implement
// the above approach
class GFG {
 
    // Function to return sum of
    // N term of the series
    static int findSum(int N) {
        return (int) (Math.pow(3, N) - Math.pow(N, 2) + 11 * N - 1);
    }
 
    // Driver Code
    public static void main(String args[]) {
        int N = 5;
        System.out.print(findSum(N));
    }
}
 
// This code is contributed by saurabh_jaiswal.

Python3

# Python code for the above approach
 
# Function to return sum of
# N term of the series
def findSum(N):
    return ((3 ** N) -
        (N ** 2) +
        11 * N - 1);
 
# Driver Code
 
# Get the value of N
N = 5;
print(findSum(N));
 
# This code is contributed by Saurabh Jaiswal

C#

// C# program to implement
// the above approach
using System;
class GFG
{
 
  // Function to return sum of
    // N term of the series
    static int findSum(int N) {
        return (int) (Math.Pow(3, N) - Math.Pow(N, 2) + 11 * N - 1);
    }
 
  // Driver Code
  public static void Main()
  {
    int N = 5;
    Console.Write(findSum(N));
 
  }
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript

        // JavaScript code for the above approach
 
        // Function to return sum of
        // N term of the series
        function findSum(N) {
            return (Math.pow(3, N) -
                Math.pow(N, 2) +
                11 * N - 1);
        }
        // Driver Code
 
        // Get the value of N
        let N = 5;
        document.write(findSum(N));
 
  // This code is contributed by Potta Lokesh
    

输出

272

时间复杂度： O(1)

辅助空间： O(1)