Amicable Pair Number in Java

In this section, we will learn what is an amicable number and also create Java programs to check if the given number is an amicable number or not. The amicable number program frequently asked in Java coding tests and academics.

Amicable Number

The amicable numbers are two different numbers (a pair of numbers) so related that the sum of the proper divisors (excluding the number itself) of one of the numbers is equal to the other. A proper divisor of a number is a divisor other than the number itself. It is also known as friendly numbers.

The smallest pair of amicable numbers is (220, 284). Because:

The divisor of 220 are: 1,2,4,5,10,11,20,22,44,55,and 110

The sum of divisor of 220 is = 284

The divisor of 284 are: 1,2,4,71,142

The sum of divisor of 284 is = 220

We observe that the sum of the divisors of the first number is equal to the second number, and the sum of divisor of the second number is equal to the first number. Hence, the given pair (220, 284) is an amicable pair.

Amicable Numbers Example

Some other amicable pair numbers are (10744, 10856), (12285, 14595), (17296, 18416), (63020, 76084), and (66928, 66992).

Steps to Find Amicable Number

1. Read or initialize two numbers (N1, N2) from the user.
2. Find the divisor (divOfN1, divOfN2) of both numbers.
3. Find the sum of divisors (sumdiv1, sumdiv2) of both numbers.
4. Check if the sum of divisors of one number is equal to the other number or not.
   • If equal, the pair of numbers is amicable.
   • Else, not amicable.

Let's implement the above steps in a Java program.

Amicable Number Java Program

The logic is very easy. First, we will compare the sum of both numbers and compare the sum for one number with the second number.

AmicableNumberExample1.java

Output 1:

Enter the first number: 5020
Enter the second number: 5564
5020, 5564 are amicable numbers.

Output 2:

Enter the first number: 12
Enter the second number: 45
12, 45 are not amicable numbers.

Let's create another Java program by using a different logic.

AmicableNumberExample2.java

Output 1:

Enter the first number: 220
Enter the second number: 284
The pair of numbers are amicable.

Output 2:

Enter the first number: 60
Enter the second number: 84
The pair of numbers are not amicable.