Java: Check if a number is Mersenne number or not
Java Numbers: Exercise-22 with Solution
Write a program to check if a number is a Mersenne number or not.
In mathematics, a Mersenne number is a number that can be written in the form M(n) = 2n − 1 for some integer n.
The first four Mersenne primes are 3, 7, 31, and 127
Test Data
Input a number: 127
Pictorial Presentation:
Sample Solution:
Java Code:
import java.util.Scanner;
import java.math.BigInteger;
public class Example22 {
public static void main(String args[])
{
Scanner in = new Scanner(System.in);
System.out.print("Input a number: ");
int n = in.nextInt();
int n1 = n + 1;
int power = 0;
int ans = 0;
for(int i=0;;i++)
{
power=(int)Math.pow(2,i);
if(power>n1)
{
break;
}
else if(power==n1)
{
System.out.println(n+" is a Mersenne number.");
ans=1;
}
}
if(ans==0)
{
System.out.println(n+" is not a Mersenne number.");
}
}
}
Sample Output:
Input a number: 127 127 is a Mersenne number.
Flowchart:

Java Code Editor:
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Java: Tips of the Day
IsPowerOfTwo
Checks if a value is positive power of two.
To understand how it works let's assume we made a call IsPowerOfTwo(4).
As value is greater than 0, so right side of the && operator will be evaluated.
The result of (~value + 1) is equal to value itself. ~100 + 001 => 011 + 001 => 100. This is equal to value.
The result of (value & value) is value. 100 & 100 => 100.
This will value the expression to true as value is equal to value.
public static boolean isPowerOfTwo(final int value) { return value > 0 && ((value & (~value + 1)) == value); }
Ref: https://bit.ly/3sA5d4I
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