Sum of amicable numbers

[Sam Benry]

Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.

For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

Evaluate the sum of all the amicable numbers under 10000.

whats wrong with this code?

public static int sumOfDivisors(int number)
{
int sum=0;
for(int i=1;i<number;i++)
if (number % i == 0) 
sum += i;
return sum;
}
public static boolean isAmicable(int number)
{
int a = sumOfDivisors(number);
int b = sumOfDivisors(a);
if (a == sumOfDivisors(b)) return true;
else return false;
}
public static void main(String[] args) 
{
long sum = 0 ;
for (int i=0;i<10000;i++)
if (isAmicable(i)) sum+=i;
System.out.println(sum);
}

[Joanne Neal]

What makes you think there is something wrong ? If it doesn't compile then post the exact error messages with an indication of what line they refer to. If it doesn't do what you expect then tell us what it is doing and how this differs from what you want it to do.

[Sam Benry]

the answer its returning is 73304
which is wrong...
but I have no idea why it is wrong, I THINK it has something to do with the condition

if (a == sumOfDivisors(b)) return true;

but im not sure...

[Rob Spoor]

Let's take your example.

isAmicable(220):
int a = sumOfDivisors(220); 284
int b = sumOfDivisors(a); // should be 220
return b == number; // because that's what you have to check for

[Sam Benry]

gives 40284, but still this is the wrong answer
:S
this is really confusing

[Ulf Dittmer]

How do you know that's the wrong answer?

[Sam Benry]

its a problem from Project Euler, i googled around and found out that the correct answer is 31626

but donno why the code is giving a wrong answer...
does anyone have any idea? or at least an alternative method to solve this?

[Paul Clapham]

So you have this number 40284 and you don't know where it came from. Well, you do know, it came from your code, but the problem is you don't know why the code came up with that number.

As I see it, your code simply adds up all the numbers in a range for which the isAmicable method returns true. So if it doesn't produce the sum of all numbers in that range that are amicable numbers, then the isAmicable method isn't always correctly reporting which numbers are amicable. How would you go about investigating that?

[Sam Benry]

yeah i guess that and said that there might be a problem in the conditions of the isAmicable, but the problem is I'm not able to correct it...
I tried alot, but it just wont work, whats the mistake there?

[Paul Clapham]

As I see it, the problem is that you don't know what numbers it classifies as amicable. You don't see any way to find that out?

[Sam Benry]

I am blind, the code is fine, the problem is to add this (&& a != b)
to the conditional
thanks all

[Paul Clapham]

That's right. Translated into the language of the problem, perfect numbers are not amicable numbers.