Encuentra el término N de la serie 4, 2, 2, 3, 6, …

Dado un número N , la tarea es encontrar el N-ésimo término en la serie 4, 2, 2, 3, 6, …
Ejemplo: 
 

Input: N = 2
Output: 2

Input: N = 5
Output: 6

Acercarse:

• El enésimo número de la serie se obtiene por 
  1. Multiplicar el número anterior por la posición del propio número anterior.
  2. Divide el número obtenido por 2.
• Como el número inicial de la serie es 4 

1st term = 4
2nd term = (4 * 1) / 2 = 2
3rd term = (2 * 2) / 2 = 2
4th term = (2 * 3) / 2 = 3
5th term = (3 * 4) / 2 = 6
And, so on....

• En general, el número N se obtiene mediante la fórmula: 
   

A continuación se muestra la implementación del enfoque anterior: 
 

// C++ program to find Nth term
// of the series 4, 2, 2, 3, 6, ...
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find Nth term
int nthTerm(int N)
{
    int nth = 0, first_term = 4;
 
    int pi = 1, po = 1;
    int n = N;
    while (n > 1) {
        pi *= n - 1;
        n--;
        po *= 2;
    }
 
    // Nth term
    nth = (first_term * pi) / po;
 
    return nth;
}
 
// Driver code
int main()
{
    int N = 5;
 
    cout << nthTerm(N) << endl;
 
    return 0;
}

// Java program to find Nth term
// of the series 4, 2, 2, 3, 6, ...
class GFG
{
 
// Function to find Nth term
static int nthTerm(int N)
{
    int nth = 0, first_term = 4;
 
    int pi = 1, po = 1;
    int n = N;
    while (n > 1)
    {
        pi *= n - 1;
        n--;
        po *= 2;
    }
 
    // Nth term
    nth = (first_term * pi) / po;
 
    return nth;
}
 
// Driver code
public static void main(String[] args)
{
    int N = 5;
 
    System.out.print(nthTerm(N) +"\n");
}
}
 
// This code is contributed by Rajput-Ji

# Python3 program to find Nth term
# of the series 4, 2, 2, 3, 6, ...
 
# Function to find Nth term
def nthTerm(N) :
 
    nth = 0; first_term = 4;
 
    pi = 1; po = 1;
    n = N;
    while (n > 1) :
        pi *= n - 1;
        n -= 1;
        po *= 2;
 
    # Nth term
    nth = (first_term * pi) // po;
 
    return nth;
 
# Driver code
if __name__ == "__main__" :
    N = 5;
    print(nthTerm(N)) ;
 
# This code is contributed by AnkitRai01

// C# program to find Nth term
// of the series 4, 2, 2, 3, 6, ...
using System;
 
class GFG
{
 
// Function to find Nth term
static int nthTerm(int N)
{
    int nth = 0, first_term = 4;
 
    int pi = 1, po = 1;
    int n = N;
    while (n > 1)
    {
        pi *= n - 1;
        n--;
        po *= 2;
    }
 
    // Nth term
    nth = (first_term * pi) / po;
 
    return nth;
}
 
// Driver code
public static void Main(String[] args)
{
    int N = 5;
 
    Console.Write(nthTerm(N) +"\n");
}
}
 
// This code is contributed by PrinciRaj1992

<script>
    // Javascript program to find Nth term
    // of the series 4, 2, 2, 3, 6, ...
     
    // Function to find Nth term
    function nthTerm(N)
    {
        let nth = 0, first_term = 4;
 
        let pi = 1, po = 1;
        let n = N;
        while (n > 1) {
            pi *= n - 1;
            n--;
            po *= 2;
        }
 
        // Nth term
        nth = (first_term * pi) / po;
 
        return nth;
    }
   
      let N = 5;
    document.write(nthTerm(N));
 
// This code is contributed by divyeshrabadiya07.
</script>

6

Complejidad de tiempo : O (N) para la entrada dada N

Espacio Auxiliar: O(1)