Java Program to Check Whether a Number is a Strong Number

A Strong Number is a number where the sum of the factorials of its digits equals the number itself. For example, the number 145 is a Strong Number because

• The factorial of 1 is 1 (1! = 1)
• The factorial of 4 is 24 (4! = 24)
• The factorial of 5 is 120 (5! = 120)
• The sum is 1 + 24 + 120 = 145, which is equal to the original number.

So, 145 is a Strong Number.

Steps to Check if a Number is a Strong Number

1. Extract the digits: Break the number down into its digits.
2. Find the factorial of each digit: Calculate the factorial of each digit.
3. Add the factorials: Add up the factorials of the digits.
4. Compare the sum: If the sum of the factorials is the same as the original number, it is a Strong Number.

Java Program

import java.util.Scanner;

public class StrongNumber {
    
    // Function to calculate the factorial of a number
    public static int factorial(int num) {
        int fact = 1;
        for (int i = 1; i <= num; i++) {
            fact *= i;
        }
        return fact;
    }
    
    // Function to check if the number is a Strong Number
    public static boolean isStrongNumber(int number) {
        int originalNumber = number;  // Store the original number
        int sum = 0;  // Store the sum of factorials
        
        // Extract each digit of the number
        while (number > 0) {
            int digit = number % 10;  // Get the last digit
            sum += factorial(digit);  // Add the factorial of the digit to the sum
            number /= 10;  // Remove the last digit
        }
        
        // Check if the sum equals the original number
        return sum == originalNumber;
    }
    
    public static void main(String[] args) {
        // Create a scanner to read user input
        Scanner scanner = new Scanner(System.in);
        
        // Ask the user to input a number
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        
        // Check if the number is a Strong Number
        if (isStrongNumber(num)) {
            System.out.println(num + " is a Strong Number.");
        } else {
            System.out.println(num + " is not a Strong Number.");
        }
        
        // Close the scanner
        scanner.close();
    }
}

How does the Program Work?

1. Factorial Function: The factorial(int num) method calculates the factorial of a number. It multiplies all numbers from 1 to
2. Checking for Strong Number: The isStrongNumber(int number) method checks if the number is a Strong Number. It does this by.
   • Extracting each digit of the number using the modulus (%) operator.
   • Calculating the factorial of each digit.
   • Adding the factorials together.
   • Finally, compare the sum with the original number.
3. Main Program: In the main() method, the user is asked to enter a number. This number is then checked using the isStrongNumber() method. The program prints whether the number is a Strong Number or not.

Example Outputs

Example 1

1. Input: 145
2. Output
   

Example 2

1. Input: 123
2. Output
   

Conclusion

A Strong Number is a number where the sum of the factorials of its digits is equal to the number itself. This Java program helps us check whether a number is a Strong Number by breaking the number down into its digits, finding the factorial of each digit, and comparing the sum to the original number. This task is a great way to practice loops, functions, and math operations in Java.