In this article, we are going to find whether a number is `perfect`

or not using Java.

Table of Contents

A number is called a

`perfect number`

if the sum of its divisors is equal to the number. The sum of divisors excludes the number. There may be several approaches to find the perfect number.**For example:**

– 28’s divisors are 1, 2, 4, 7, 14

– sum of divisors of 28 excluding itself is 28.

**Recommended read**

Here, we are using two main approaches iterative and recursive approach.

Let’s see the example.

## Iterative approach

In this example, we are using the while loop to find divisors of the number and then get sum of them.

Here are the steps:

- Initiaze
`sum=0`

and loop variable`i=1`

. - Iterate a while loop until condition
`i<=number/2`

is false. - Check remainder of
`number%i`

using modulo operator. If remainder is 0, then add it to the`sum`

. - If
`sum`

is equals to number after all iterations, then it is`perfect number`

.

12345678910111213141516171819202122public class Main{public static void main(String args[]){int number = 28;int sum = 0;int i = 1;while(i<=number/2){if(number%i == 0){sum+=i;}i++;}if(sum == number)System.out.println("It is Perfect Number");else System.out.println("It is not Perfect Number");}}

Output

## Recursive approach

We can use recursion technique, if don’t want to use while loop. It reduces code statements but provides the accurate result.

Here are the steps:

- Initialize static variable
`sum=0`

. - Create a function
`findPerfect()`

which will take two parameters`number`

and`div`

- Check if
`div<=number/2`

is true. This will be the terminal condition for recursion.- Check remainder of
`number%i`

using modulo operator. If remainder is 0, then add it to the`sum`

. - Increment
`div`

- Call
`findPerfect()`

recursively.

- Check remainder of
- If returned output of
`findPerfect()`

is equals to number, then it is`perfect number`

.

See the example below.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 |
public class Main { static int number = 8128; static int sum = 0; static int div = 1; static int findPerfect(int number, int div) { { if(div<=number/2) { if(number%div==0) { sum+=div; } div++; findPerfect(number,div); } return sum; } } public static void main(String args[]) { int result = findPerfect(number,div); if(result == number) System.out.println("It is Perfect Number"); else System.out.println("It is not Perfect Number"); } } |

Output

That’s all about how to find Perfect Number in Java.