# Frequently Asked Java Program 28: Java Program to Find if Given Number Is a Perfect Number

### Perfect Number:

A Perfect number is a positive integer that is equal to the sum of its proper divisors excluding the number itself.

For Example: Take Number 6. Its divisors are 1, 2 , 3 and 6. When we add all divisors except 6 ( as it is number itself) (i.e. 1+2+3= 6), it is equal to actual number. So we can say Number 6 is a perfect number.

The smallest perfect number is 6. Other perfect numbers are 28, 496, and 8,128.

Logic:

- When we divide a number say X by other number say Y and reminder is zero, then number Y is a proper divisor. All proper divisor of a number X are between 1 and X/2. ( 1 and X/2 are included) . To find the proper divisor we need to divide the number by 1 to number/2.
- We need to keep adding all divisors.

Java Program:

package StringPrograms; import java.util.Scanner; public class PerfectNumber { public static void perfectNumber(int userInput) { // Handling numbers less than or equal to zero if(userInput<=0) { System.out.println("A perfect number must be positive and greater than zero. So kindly enter number greater than zero."); } else { int sum =0; // Iterating till half of the number for(int i = 1; i<= userInput/2;i++) { // If number is divisible, add divisor. if(userInput%i==0) { sum = sum+i; } } // If sum is equal to number if(userInput==sum) { System.out.println(userInput+" is a perfect number."); } else { System.out.println(userInput+" is not a perfect number."); } } } public static void main(String[] args) { // User input for the number Scanner sc = new Scanner(System.in); System.out.println("Please enter the number to check for perfect number : "); int userInput = sc.nextInt(); sc.close(); System.out.println("You entered: " + userInput); perfectNumber(userInput); } }

Output:

[java]

Please enter the number to check for perfect number :

6

You entered: 6

6 is a perfect number.

=====================================================

Please enter the number to check for perfect number :

1

You entered: 1

1 is not a perfect number.

====================================================

Please enter the number to check for perfect number :

-10

You entered: -10

A perfect number must be positive and greater than zero. So kindly enter number greater than zero.

======================================================

Please enter the number to check for perfect number :

10

You entered: 10

10 is not a perfect number.

[/java]

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