Strong Number in Java | Concept and Its Implementation


In this article, we will delve into the world of strong number in Java, exploring their definition, properties, and implementation.

Java, one of the most popular programming languages, offers a plethora of mathematical concepts to enhance the functionality of your programs. One such concept is “strong numbers.”

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Whether you’re a novice programmer or an experienced developer, this guide will equip you with the knowledge to leverage strong numbers effectively in your Java projects.

Strong Number in Java: What Is It?

A strong number, also known as a strong or digital factorial, is a special type of number that holds a fascinating property. Let’s break it down:

Definition of Strong Number

A positive integer is considered a strong number if the sum of the factorial of its digits is equal to the number itself. In other words, if we have an integer “n,” the sum of the factorial of its individual digits should equal “n.”

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Example of a Strong Number

Let’s take the number 145 as an example to understand the concept better:

1! + 4! + 5! = 1 + 24 + 120 = 145

As you can see, the sum of the factorials of the digits (1, 4, and 5) equals the number itself (145). Thus, 145 is a strong number.

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Understanding Factorial and Its Calculation

Before we proceed further, it’s essential to comprehend the concept of factorial as it forms the basis for strong numbers.

Factorial Definition

The factorial of a non-negative integer “n” is the product of all positive integers less than or equal to “n.” It is denoted by “n!”.

Factorial Calculation Example

For instance, let’s calculate the factorial of 5:

5! = 5 × 4 × 3 × 2 × 1 = 120

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Verifying Strong Numbers in Java

Now that we grasp the essence of strong numbers, let’s move on to verifying whether a given number is strong or not using Java programming.

Steps to Check for a Strong Number

To determine if a number “num” is strong, follow these steps:

  1. Separate the digits of the number.
  2. Calculate the factorial of each digit.
  3. Sum the factorials of all digits.
  4. Compare the sum with the original number.

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Java Implementation

// Java Program to check for a Strong Number

public class StrongNumber {
    // Function to calculate the factorial of a number
    static int factorial(int n) {
        if (n == 0 || n == 1) return 1;
        return n * factorial(n - 1);

    // Function to check if a number is strong
    static boolean isStrong(int num) {
        int temp = num;
        int sum = 0;

        // Separate the digits and calculate the sum of their factorials
        while (temp > 0) {
            int digit = temp % 10;
            sum += factorial(digit);
            temp /= 10;

        // Check if the sum of factorials is equal to the original number
        return sum == num;

    // Main method to test the functionality
    public static void main(String[] args) {
        int num = 145;
        if (isStrong(num))
            System.out.println(num + " is a Strong Number.");
            System.out.println(num + " is not a Strong Number.");

In this example, we have created a Java program to check whether a given number (in this case, 145) is a strong number or not.

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The isStrong method first separates the digits of the number and then calculates the sum of their factorials. Finally, it compares the sum with the original number to determine if it is a strong number.

Properties of Strong Numbers

Strong numbers possess some interesting properties that make them worth exploring further. Let’s delve into these properties:

1. Existence of Strong Numbers

One fascinating property of strong numbers is that they do exist! Though they may not be as abundant as prime numbers, there are still numerous strong numbers to be discovered.

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2. Upper Bound

Strong numbers are not boundless. As you increase the number of digits in a strong number, it becomes more challenging to find them. However, powerful algorithms can be designed to compute them efficiently.

3. Multiplicity

Unlike prime numbers, where each number is either prime or not, strong numbers have a concept of multiplicity. A number can be more than one strong number if it meets the strong number criteria for multiple permutations of its digits.

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4. Relationship with Other Numbers

Strong numbers are related to several other mathematical concepts, including perfect numbers and armstrong numbers. Exploring these relationships can provide a deeper understanding of number theory.

Applications of Strong Numbers

The concept of strong numbers, though intriguing in itself, finds applications in various practical scenarios:

1. Error Detection

In error-detection mechanisms, strong numbers can be used to identify discrepancies in data transmissions. By using strong numbers as checksums, errors introduced during data transfer can be detected and corrected.

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2. Cryptography

Strong numbers play a role in certain cryptographic algorithms, where they help generate secure keys and ensure data integrity during encryption and decryption processes.

3. Puzzle and Game Development

Strong numbers can be employed in puzzle creation or game development, where specific strong numbers act as critical components of puzzle solutions or game mechanics.

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Frequently Asked Questions (FAQs)

1. What are the first few strong numbers?

Some of the first few strong numbers are 1, 2, 145, 40585, and 871.

2. Can a negative number be a strong number?

No, strong numbers are defined only for positive integers.

3. How do strong numbers differ from perfect numbers?

While both strong and perfect numbers have special properties, the criteria for their determination are distinct. Strong numbers rely on the sum of factorial of digits, whereas perfect numbers rely on the sum of proper divisors.

4. Is zero (0) a strong number?

No, zero is not considered a strong number as it does not meet the criteria of having positive digits.

5. How can strong numbers be useful in coding interviews?

In coding interviews, questions related to strong numbers can test a candidate’s problem-solving skills and understanding of number theory.

6. Are strong numbers relevant in real-world applications?

Yes, strong numbers have practical applications in error detection, cryptography, and puzzle or game development.


In conclusion, strong numbers in Java present an exciting avenue to explore number theory and enhance your programming skills.

Understanding the concept of strong numbers, calculating factorials, and implementing algorithms to verify their existence empowers you to solve complex problems in various domains.

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So, go ahead and leverage strong numbers to add a touch of mathematical magic to your Java programs. By incorporating them intelligently, you can develop robust applications with enhanced functionality and error-detection capabilities.

Remember, practice is key, and the more you experiment with strong numbers, the better you’ll become at employing them efficiently in your Java coding endeavors.