# Find the sum of series 3, -6, 12, -24 . . . upto N terms

• Last Updated : 23 Jun, 2022

Given an integer N. The task is to find the sum upto N terms of the given series:

3, -6, 12, -24, … upto N terms

Examples

Input : N = 5
Output : Sum = 33

Input : N = 20
Output : Sum = -1048575

On observing the given series, it can be seen that the ratio of every term with their previous term is same which is -2. Hence the given series is a GP(Geometric Progression) series.
So, when r < 0.
In above GP series the first term i:e a = 3 and common ratio i:e r = (-2).
Therefore,
Thus, .
Below is the implementation of above approach:

## C++

 //C++ program to find sum upto N term of the series:// 3, -6, 12, -24, ..... #include#includeusing namespace std;//calculate sum upto N term of series class gfg{    public:    int Sum_upto_nth_Term(int n)    {        return (1 - pow(-2, n));    }};// Driver codeint main(){    gfg g;    int N = 5;    cout<

## Java

 //Java program to find sum upto N term of the series:// 3, -6, 12, -24, ..... import java.util.*;//calculate sum upto N term of series class solution{ static int Sum_upto_nth_Term(int n){    return (1 -(int)Math.pow(-2, n));} // Driver codepublic static void main (String arr[]){    int N = 5;    System.out.println(Sum_upto_nth_Term(N));} }

## Python

 # Python program to find sum upto N term of the series:# 3, -6, 12, -24, ..... # calculate sum upto N term of seriesdef Sum_upto_nth_Term(n):    return (1 - pow(-2, n)) # Driver codeN = 5print(Sum_upto_nth_Term(N))

## C#

 // C# program to find sum upto// N term of the series:// 3, -6, 12, -24, ..... // calculate sum upto N term of seriesclass GFG{ static int Sum_upto_nth_Term(int n){    return (1 -(int)System.Math.Pow(-2, n));} // Driver codepublic static void Main(){    int N = 5;    System.Console.WriteLine(Sum_upto_nth_Term(N));}} // This Code is contributed by mits

## PHP

 

## Javascript

 

Output:

33`

Time Complexity: O(logn), where n is the given integer.

Auxiliary Space: O(1), no extra space is required, so it is a constant.

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