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Mersenne Prime
• Difficulty Level : Easy
• Last Updated : 26 Mar, 2021

Mersenne Prime is a prime number that is one less than a power of two. In other words, any prime is Mersenne Prime if it is of the form 2k-1 where k is an integer greater than or equal to 2. First few Mersenne Primes are 3, 7, 31 and 127.
The task is print all Mersenne Primes smaller than an input positive integer n.
Examples:

```Input: 10
Output: 3 7
3 and 7 are prime numbers smaller than or
equal to 10 and are of the form 2k-1

Input: 100
Output: 3 7 31 ```

The idea is to generate all the primes less than or equal to the given number n using Sieve of Eratosthenes. Once we have generated all such primes, we iterate through all numbers of the form 2k-1 and check if they are primes or not.
Below is the implementation of the idea.

## C++

 `// Program to generate mersenne primes``#include``using` `namespace` `std;` `// Generate all prime numbers less than n.``void` `SieveOfEratosthenes(``int` `n, ``bool` `prime[])``{``    ``// Initialize all entries of boolean array``    ``// as true. A value in prime[i] will finally``    ``// be false if i is Not a prime, else true``    ``// bool prime[n+1];``    ``for` `(``int` `i=0; i<=n; i++)``        ``prime[i] = ``true``;` `    ``for` `(``int` `p=2; p*p<=n; p++)``    ``{``        ``// If prime[p] is not changed, then it``        ``// is a prime``        ``if` `(prime[p] == ``true``)``        ``{``            ``// Update all multiples of p``            ``for` `(``int` `i=p*2; i<=n; i += p)``                ``prime[i] = ``false``;``        ``}``    ``}``}` `// Function to generate mersenne primes less``// than or equal to n``void` `mersennePrimes(``int` `n)``{``    ``// Create a boolean array "prime[0..n]"``    ``bool` `prime[n+1];` `    ``// Generating primes using Sieve``    ``SieveOfEratosthenes(n,prime);` `    ``// Generate all numbers of the form 2^k - 1``    ``// and smaller than or equal to n.``    ``for` `(``int` `k=2; ((1<

## Java

 `// Program to generate``// mersenne primes``import` `java.io.*;` `class` `GFG {``    ` `    ``// Generate all prime numbers``    ``// less than n.``    ``static` `void` `SieveOfEratosthenes(``int` `n,``                          ``boolean` `prime[])``    ``{``        ``// Initialize all entries of``        ``// boolean array as true. A``        ``// value in prime[i] will finally``        ``// be false if i is Not a prime,``        ``// else true bool prime[n+1];``        ``for` `(``int` `i = ``0``; i <= n; i++)``            ``prime[i] = ``true``;``    ` `        ``for` `(``int` `p = ``2``; p * p <= n; p++)``        ``{``            ``// If prime[p] is not changed``            ``// , then it is a prime``            ``if` `(prime[p] == ``true``)``            ``{``                ``// Update all multiples of p``                ``for` `(``int` `i = p * ``2``; i <= n; i += p)``                    ``prime[i] = ``false``;``            ``}``        ``}``    ``}``    ` `    ``// Function to generate mersenne``    ``// primes lessthan or equal to n``    ``static` `void` `mersennePrimes(``int` `n)``    ``{``        ``// Create a boolean array``        ``// "prime[0..n]"``        ``boolean` `prime[]=``new` `boolean``[n + ``1``];``    ` `        ``// Generating primes``        ``// using Sieve``        ``SieveOfEratosthenes(n, prime);``    ` `        ``// Generate all numbers of``        ``// the form 2^k - 1 and``        ``// smaller than or equal to n.``        ``for` `(``int` `k = ``2``; (( ``1` `<< k) - ``1``) <= n; k++)``        ``{``            ``long` `num = ( ``1` `<< k) - ``1``;``    ` `            ``// Checking whether number is``            ``// prime and is one less then``            ``// the power of 2``            ``if` `(prime[(``int``)(num)])``                ``System.out.print(num + ``" "``);``        ``}``    ``}``    ` `    ``// Driven program``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `n = ``31``;``        ``System.out.println(``"Mersenne prime"``+``                     ``"numbers smaller than"``+``                          ``"or equal to "``+n);``        ` `        ``mersennePrimes(n);``    ``}``}` `// This code is contributed by Nikita Tiwari.`

## Python3

 `# Program to generate mersenne primes` `# Generate all prime numbers``# less than n.``def` `SieveOfEratosthenes(n, prime):` `    ``# Initialize all entries of boolean``    ``# array as true. A value in prime[i]``    ``# will finally be false if i is Not``    ``# a prime, else true bool prime[n+1]``    ``for` `i ``in` `range``(``0``, n ``+` `1``) :``        ``prime[i] ``=` `True` `    ``p ``=` `2``    ``while``(p ``*` `p <``=` `n):``    ` `        ``# If prime[p] is not changed,``        ``# then it is a prime``        ``if` `(prime[p] ``=``=` `True``) :``        ` `            ``# Update all multiples of p``            ``for` `i ``in` `range``(p ``*` `2``, n ``+` `1``, p):``                ``prime[i] ``=` `False``                ` `        ``p ``+``=` `1``        ` `# Function to generate mersenne``# primes less than or equal to n``def` `mersennePrimes(n) :` `    ``# Create a boolean array``    ``# "prime[0..n]"``    ``prime ``=` `[``0``] ``*` `(n ``+` `1``)` `    ``# Generating primes using Sieve``    ``SieveOfEratosthenes(n, prime)` `    ``# Generate all numbers of the``    ``# form 2^k - 1 and smaller``    ``# than or equal to n.``    ``k ``=` `2``    ``while``(((``1` `<< k) ``-` `1``) <``=` `n ):``    ` `        ``num ``=` `(``1` `<< k) ``-` `1` `        ``# Checking whether number``        ``# is prime and is one``        ``# less then the power of 2``        ``if` `(prime[num]) :``            ``print``(num, end ``=` `" "` `)``            ` `        ``k ``+``=` `1``    ` `# Driver Code``n ``=` `31``print``(``"Mersenne prime numbers smaller"``,``              ``"than or equal to "` `, n )``mersennePrimes(n)` `# This code is contributed``# by Smitha`

## C#

 `// C# Program to generate mersenne primes``using` `System;` `class` `GFG {``    ` `    ``// Generate all prime numbers less than n.``    ``static` `void` `SieveOfEratosthenes(``int` `n,``                                ``bool` `[]prime)``    ``{``        ` `        ``// Initialize all entries of``        ``// boolean array as true. A``        ``// value in prime[i] will finally``        ``// be false if i is Not a prime,``        ``// else true bool prime[n+1];``        ``for` `(``int` `i = 0; i <= n; i++)``            ``prime[i] = ``true``;``    ` `        ``for` `(``int` `p = 2; p * p <= n; p++)``        ``{``            ` `            ``// If prime[p] is not changed,``            ``// then it is a prime``            ``if` `(prime[p] == ``true``)``            ``{``                ` `                ``// Update all multiples of p``                ``for` `(``int` `i = p * 2; i <= n; i += p)``                    ``prime[i] = ``false``;``            ``}``        ``}``    ``}``    ` `    ``// Function to generate mersenne``    ``// primes lessthan or equal to n``    ``static` `void` `mersennePrimes(``int` `n)``    ``{``        ` `        ``// Create a boolean array``        ``// "prime[0..n]"``        ``bool` `[]prime = ``new` `bool``[n + 1];``    ` `        ``// Generating primes``        ``// using Sieve``        ``SieveOfEratosthenes(n, prime);``    ` `        ``// Generate all numbers of``        ``// the form 2^k - 1 and``        ``// smaller than or equal to n.``        ``for` `(``int` `k = 2; (( 1 << k) - 1) <= n; k++)``        ``{``            ``long` `num = ( 1 << k) - 1;``    ` `            ``// Checking whether number is``            ``// prime and is one less then``            ``// the power of 2``            ``if` `(prime[(``int``)(num)])``                ``Console.Write(num + ``" "``);``        ``}``    ``}``    ` `    ``// Driven program``    ``public` `static` `void` `Main()``    ``{``        ``int` `n = 31;``        ` `        ``Console.WriteLine(``"Mersenne prime numbers"``               ``+ ``" smaller than or equal to "` `+ n);``        ` `        ``mersennePrimes(n);``    ``}``}` `// This code is contributed by nitin mittal.`

## PHP

 ``

## Javascript

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Output:

```Mersenne prime numbers smaller than or equal to 31
3 7 31 ```

References:
https://en.wikipedia.org/wiki/Mersenne_prime
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