# Sum of all mersenne numbers present in an array

Given an array of integers arr[], the task is to find the sum of all the Mersenne numbers from the array. A number is a Mersenne number if it is greater than 0 and is one less than some power of 2. First few Mersenne numbers are 1, 3, 7, 15, 31, 63, 127, …

Examples:

Input: arr[] = {17, 6, 7, 63, 3}
Output: 73
Only 7, 63 and 3 are Mersenne numbers i.e. 7 + 63 + 3 = 73

Input: arr[] = {1, 3, 11, 45}
Output: 4

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Initialise sum = 0 and start traversing all the elements of the array, if current element is one less than some power of 2 and is greater than 0 then update sum = sum + arr[i]. Print the sum in the end.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function that returns true ` `// if n is a Mersenne number ` `int` `isMersenne(``int` `n) ` `{ ` `    ``while` `(n != 0)  ` `    ``{ ` `        ``int` `r = n % 2; ` `        ``if` `(r == 0) ` `            ``return` `false``; ` `        ``n /= 2; ` `    ``} ` `    ``return` `true``; ` `} ` ` `  `// Function to return the sum of all the ` `// Mersenne numbers from the given array ` `int` `sumOfMersenne(``int` `arr[], ``int` `n) ` `{ ` ` `  `    ``// To store the required sum ` `    ``int` `sum = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `    ``{ ` ` `  `        ``// If current element is a Mersenne number ` `        ``if` `(arr[i] > 0 && isMersenne(arr[i]))  ` `        ``{ ` `            ``sum += arr[i]; ` `        ``} ` `    ``} ` `    ``return` `sum; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 17, 6, 7, 63, 3 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``); ` `    ``cout << (sumOfMersenne(arr, n)); ` `    ``return` `0; ` `} ` ` `  `// This code is contributed by jit_t `

## Java

 `// Java implementation of the approach ` `class` `GFG { ` ` `  `    ``// Function that returns true ` `    ``// if n is a Mersenne number ` `    ``static` `boolean` `isMersenne(``int` `n) ` `    ``{ ` `        ``while` `(n != ``0``) { ` `            ``int` `r = n % ``2``; ` `            ``if` `(r == ``0``) ` `                ``return` `false``; ` `            ``n /= ``2``; ` `        ``} ` `        ``return` `true``; ` `    ``} ` ` `  `    ``// Function to return the sum of all the ` `    ``// Mersenne numbers from the given array ` `    ``static` `int` `sumOfMersenne(``int``[] arr, ``int` `n) ` `    ``{ ` ` `  `        ``// To store the required sum ` `        ``int` `sum = ``0``; ` `        ``for` `(``int` `i = ``0``; i < n; i++) { ` ` `  `            ``// If current element is a Mersenne number ` `            ``if` `(arr[i] > ``0` `&& isMersenne(arr[i])) { ` `                ``sum += arr[i]; ` `            ``} ` `        ``} ` `        ``return` `sum; ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int``[] arr = { ``17``, ``6``, ``7``, ``63``, ``3` `}; ` `        ``int` `n = arr.length; ` `        ``System.out.print(sumOfMersenne(arr, n)); ` `    ``} ` `} `

## Python3

 `# Python3 implementation of the approach  ` ` `  `# Function that returns true  ` `# if n is a Mersenne number  ` `def` `isMersenne(n) :  ` `    ``while` `(n !``=` `0``) : ` `        ``r ``=` `n ``%` `2``; ` `        ``if` `(r ``=``=` `0``) : ` `            ``return` `False``;  ` `        ``n ``/``/``=` `2``;  ` `         `  `    ``return` `True``;  ` ` `  `# Function to return the sum of all the  ` `# Mersenne numbers from the given array  ` `def` `sumOfMersenne(arr, n) :  ` `    ``# To store the required sum  ` `    ``sum` `=` `0``;  ` `    ``for` `i ``in` `range``(n) : ` ` `  `        ``# If current element is a Mersenne number  ` `        ``if` `(arr[i] > ``0` `and` `isMersenne(arr[i])) : ` `            ``sum` `+``=` `arr[i];  ` `     `  `    ``return` `sum``;  ` ` `  ` `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"` `:  ` ` `  `    ``arr ``=` `[``17``, ``6``, ``7``, ``63``, ``3` `]; ` `    ``n ``=` `len``(arr);  ` `    ``print``(sumOfMersenne(arr, n));  ` `     `  `# This code is contributed by AnkitRai01 `

## C#

 `//C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG ` `{ ` `    ``// Function that returns true ` `    ``// if n is a Mersenne number ` `    ``static` `bool` `isMersenne(``int` `n) ` `    ``{ ` `        ``while` `(n != 0)  ` `        ``{ ` `            ``int` `r = n % 2; ` `            ``if` `(r == 0) ` `                ``return` `false``; ` `            ``n /= 2; ` `        ``} ` `        ``return` `true``; ` `    ``} ` ` `  `    ``// Function to return the sum of all the ` `    ``// Mersenne numbers from the given array ` `    ``static` `int` `sumOfMersenne(``int``[] arr, ``int` `n) ` `    ``{ ` ` `  `        ``// To store the required sum ` `        ``int` `sum = 0; ` `        ``for` `(``int` `i = 0; i < n; i++)  ` `        ``{ ` ` `  `            ``// If current element is a Mersenne number ` `            ``if` `(arr[i] > 0 && isMersenne(arr[i])) ` `            ``{ ` `                ``sum += arr[i]; ` `            ``} ` `        ``} ` `        ``return` `sum; ` `    ``} ` ` `  `    ``// Driver code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `        ``int``[] arr = { 17, 6, 7, 63, 3 }; ` `        ``int` `n = arr.Length; ` `        ``Console.WriteLine(sumOfMersenne(arr, n)); ` `    ``} ` `} ` ` `  `// This code is contributed by jit_t `

Output:

```73
```

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : jit_t, AnkitRai01