check if a number is a perfect number in Java

Mathematics for Programming Numbers (Article) Numbers (Program)

35

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Given Input:

28

Expected Output:

28 is a perfect number.

Program:

public class PerfectNumberChecker {
    public static boolean isPerfectNumber(int number) {
        if (number <= 1) {
            return false; // Perfect numbers are positive integers greater than 1
        }
        
        int sum = 1; // Start with 1 as 1 is always a divisor

        // Find all divisors up to the square root of the number
        for (int i = 2; i * i <= number; i++) {
            if (number % i == 0) {
                sum += i; // i is a divisor
                if (i != number / i) {
                    sum += number / i; // number / i is also a divisor (if it's different)
                }
            }
        }

        // If sum of divisors equals the number, then it's a perfect number
        return sum == number;
    }

    public static void main(String[] args) {
        int number = 28; // Example number to check
        if (isPerfectNumber(number)) {
            System.out.println(number + " is a perfect number.");
        } else {
            System.out.println(number + " is not a perfect number.");
        }
    }
}

Output:

28 is a perfect number.

Explanation:

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