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# C++ program to find nth Term of the Series 1 2 2 4 4 4 4 8 8 8 8 8 8 8 8 …

In this problem, we are given an integer N. Our task is to create a program to Find Nth term of series 1, 2, 2, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8…

**Let’s take an example to understand the problem,**

## Input

N = 7

## Output

4

## Solution Approach

A simple approach to solve the problem is using a loop to find the term at the nth position. The terms will be updated by doubling after each iteration. And adding it to the term counter.

**Program to illustrate the working of our solution,**

## Example

#include <iostream> using namespace std; int calcNthTerm(int N) { int termCounter = 0, termValue = 1; while (termCounter < N) { termCounter += k; termValue *= 2; } return termValue / 2; } int main() { int N = 10; cout<<N<<"th term of the series is "<<calcNthTerm(N); return 0; }

## Output

10th term of the series is 8

## Efficient Approach

An efficient approach to solve the problem is by finding the general term of the series.

Here, are terms and their last index, 1 -> last index = 1. 2 -> last index = 3. 4 -> last index = 7. 8 -> last index = 15. . . T(N) -> last index = 2*(T(N)) - 1 Also, T(N) is always of a power of 2, i.e. T(N) = 2m 2m lies in the series till the index 2^{m+1}-1.

To find the term we can calculate the value of 2^{(m)} - 1 using N.

This makes 2^{m} - 1 < N.

2^{m}- 1 < N So, m < log^{2}(N + 1)

**Program to illustrate the working of our solution,**

## Example

#include <iostream> #include <math.h> using namespace std; int calcNthTerm(int N) { return ( pow(2, (floor)(log(N + 1) / log(2)) ) ) ; } int main() { int N = 10; cout<<N<<"th term of the series is "<<calcNthTerm(N); return 0; }

## Output

10th term of the series is 8

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