求系列 2、8、18、32、50…的第 N 项

给定数列 2、8、18、32、50……，求数列的第 N 项。

例子：

Input: N = 1
Output: 2

Input: N = 3
Output: 18

Input: N = 5
Output: 50

方法：

为了找到第 n 项，我们需要找到 n 与每个项之间的关系。

1st term = 2 =  2*(1²) // 2*first perfect square

2nd term = 8 = 2*(2²) // 2*second perfect square

3rd term = 18 = 2*(3²) //  2*third perfect square

4th term = 32 = 2*(4²) //  2*fourth perfect square

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Nth term = 2*(Nth perfect square)

公式-

T_N = 2 * N ^ 2

插图-

Input: N = 5
Output: 50
Explanation-
T_N = 2 * N ^ 2
     = 2* 5 ^ 2
     = 2 * 25
     = 50

下面是实现上述方法的 C++ 程序——

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Find n-th term of series
// 2, 8, 18, 32, 50...
int nthTerm(int N)
{
 
    // Nth perfect square is N * N
    int Nthperfectsquare = N * N;
 
    return 2 * Nthperfectsquare;
}
// Driver code
int main()
{
    int N = 5;
 
    cout << nthTerm(N) << endl;
    return 0;
}

Java

// Java code for the above approach
 
import java.io.*;
 
class GFG {
   
// Find n-th term of series
// 2, 8, 18, 32, 50...
static int nthTerm(int N)
{
 
    // Nth perfect square is N * N
    int Nthperfectsquare = N * N;
 
    return 2 * Nthperfectsquare;
}
// Driver code
    public static void main (String[] args) {
       
       int N = 5;
 
        System.out.println(nthTerm(N));
    }
}
// This code is contributed by Potta Lokesh

Python

# Python program to implement
# the above approach
 
# Find n-th term of series
# 2, 8, 18, 32, 50...
def nthTerm(N):
 
    # Nth perfect square is N * N
    Nthperfectsquare = N * N
 
    return 2 * Nthperfectsquare
 
# Driver Code
if __name__ == "__main__":
   
    N = 5
     
    print(nthTerm(N))
 
# This code is contributed by Samim Hossain Mondal.

C#

using System;
 
public class GFG{
 
// Find n-th term of series
// 2, 8, 18, 32, 50...
static int nthTerm(int N)
{
 
    // Nth perfect square is N * N
    int Nthperfectsquare = N * N;
 
    return 2 * Nthperfectsquare;
}
 
// Driver code
static public void Main (){
 
    int N = 5;
    Console.Write(nthTerm(N));
}
}
 
// This code is contributed by hrithikgarg03188

Javascript

// Javascript program to implement
// the above approach
 
// Find n-th term of series
// 2, 8, 18, 32, 50...
function nthTerm(N)
{
 
    // Nth perfect square is N * N
    let Nthperfectsquare = N * N;
 
    return 2 * Nthperfectsquare;
}
 
// Driver code
let N = 5;
 
document.write(nthTerm(N))
 
// This code is contributed by gfgking.

输出：

50

时间复杂度： O(1)
辅助空间： O(1)