Problem 21 of Evaluate the sum of all the amicable numbers under 10000.

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.


public class AmicableNumbers {
	public static void main(String args[]){
		int all=0;
		for(int i=2;i<10000;i++){
			if(amicableNum(i)<10000&&amicableNum(amicableNum(i))<10000&&amicableNum(i)!=amicableNum(amicableNum(i))){
				if(i==amicableNum(amicableNum(i))){
					System.out.println("i="+i);
					System.out.println("amicableNumI="+amicableNum(i));
					System.out.println("amicableNumII="+amicableNum(amicableNum(i)));
					all+=i;
					System.out.println("inall="+all);
				}
			}
		}
		System.out.println("all="+all);
	}
	public static int amicableNum(int n){
		int sum=0;
		for(int i=n;i>1;i--){
			if(n%i==0){
				sum+=n/i;
			}
		}
		return sum;
	}
}

Answer:
31626

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