In the previous article, we have discussed Java Program to Check Cube Number

In this article we are going to understand what Mersenne number is and how we can check whether a number is Mersenne or not in Java with examples.

## Program to Check Mersenne Number

**Mersenne numbers** are numbers which can be represented in the form of 2^{n}-1.

Example :

- 63: 63 = 64-1 : 2
^{6}– 1 Mersenne number - 7: 7 = 8 – 1 : 2
^{3}– 1 Mersenne number - 9: 9 = 2
^{3}+1 : Not a Mersenne number

In the above examples the number 63 and 7 are Mersenne numbers as they are one less than exponents of 2. However 9 is not a Mersenne number.

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**Approach :**

- Enter/declare a number and store it .
- We add 1 to the number and then check if it is a exponential form of 2.
- If a match is found then the number is said to be Mersenne number.

**Program:**

import java.util.Scanner; public class MersenneNumber { public static void main(String args[]) { //Taking the number as input from the user using scanner class Scanner scan = new Scanner(System.in); System.out.print("Enter a number : "); int num = scan.nextInt(); boolean flag = false; int temp = num+1,iter=1; // Loop runs until the equivalent power is found or // Until the exponent becomes greater than the number itself while(Math.pow(2,iter)<=temp) { // Checks whether there is some equivalent power of 2 if(Math.pow(2,iter)==temp) { flag = true; break; } iter++; } if(flag) { System.out.println(num+" is a Mersenne number"); } else { System.out.println(num+" is Not a Mersenne number"); } } }

Output: Case-1 Enter a number : 63 63 is a Mersenne number Case-2 Enter a number : 27 27 is Not a Mersenne number

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