C Exercises: Check if a number is Mersenne number or not

Last update on August 05 2025 12:55:18 (UTC/GMT +8 hours)

32. Mersenne Number Check Variants

Write a program in C to check if a number is a Mersenne number or not.

Test Data
Input a number: 127

Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    int n, p, ans, i, n1; // Variables for input number, powers of 2, result, loop control, and incremented number 'n1'
    double result; // Variable to store the result of the power operation

    printf("\n\n Check whether a given number is a Mersenne number or not:\n");
    printf("------------------------------------------------------------\n");
    printf(" Input a number: ");
    scanf("%d", &n); // Reading the input number from the user

    n1 = n + 1; // Incrementing the input number by 1

    p = 0; // Initializing the variable 'p' for powers of 2
    ans = 0; // Initializing the result variable 'ans' to check if the number is a Mersenne number

    // Loop to find if 'n1' is a power of 2
    for (i = 0;; i++)
    {
        p = (int)pow(2, i); // Calculating powers of 2 using the 'pow' function

        if (p > n1)
        {
            break; // Exiting the loop if the power exceeds 'n1'
        }
        else if (p == n1)
        {
            printf(" %d is a Mersenne number.\n", n); // Printing if 'n1' is a Mersenne number
            ans = 1; // Setting the result variable to indicate 'n' is a Mersenne number
        }
    }

    if (ans == 0)
    {
        printf(" %d is not a Mersenne number.\n", n); // Printing if 'n' is not a Mersenne number
    }

    return 0; // Returning 0 to indicate successful execution
}

Sample Output:

 Input a number: 127                                                                                          
 127 is a Mersenne number.

Visual Presentation:

C programming: Check if a number is Mersenne number or not.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to check if a number is a Mersenne number by verifying it has the form 2^p - 1.
Write a C program to test Mersenne numbers using bit manipulation techniques.
Write a C program to verify Mersenne numbers and output the corresponding exponent p.
Write a C program to optimize Mersenne number checking using logarithmic functions.

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