# Mersenne prime in JavaScript

In Mathematics, a Mersenne prime is a number that can be written in the form M(n) = 2^n − 1 for some integer n and is actually a prime number.

For example − The first four Mersenne primes are 3, 7, 31, and 127

We are required to write a JavaScript function that takes in a number and checks whether it is a Mersenne prime or not. Let’s write the code for this function

## Example

const isPrime = num => {
let i = 2;
while(i <= num / 2){
if(num % i++ === 0){
return false;
};
};
return true;
}
const mersennePrime = num => {
if(!isPrime(num)){
return false;
};
let i = 0, n = num+1;
while(n !== 1){
if(n % 2 !== 0){
return false;
};
n /= 2;
};
return true;
};
console.log(mersennePrime(31));
console.log(mersennePrime(127));
console.log(mersennePrime(3));
console.log(mersennePrime(37));
console.log(mersennePrime(87));
console.log(mersennePrime(7));

## Output

The output in the console will be −

true
true
true
false
false
true

Updated on: 31-Aug-2020

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