C++ :

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
	int n,sum,t;
	cin>>n;
	for (int i=1; i<=n; i++)
	{
		sum=1,t=sqrt(i);
		for (int j=2; j<=t; j++)
			if (i%j==0) sum+=j+i/j;
		if (t*t==i) sum-=t;
		if (i==sum) cout<<i<<endl;
	}
	return 0;
}

Java :

import java.util.*;
public class Main {
    public static void main(String args[]) {
        Scanner cin = new Scanner(System.in);
        int n = cin.nextInt();
        for(int i = 2; i <= n; i ++){
            if(isPerfect(i)){
                System.out.println(i);
            }
        }
    }
    public static boolean isPerfect(int n){
        int sum = 1;
        for(int i = 2; i <= (int)Math.sqrt(n); i ++){
            if(n % i == 0){
                sum += i;
                sum += n/i;
            }
        }
        if(sum == n){
            return true;
        }else{
            return false;
        }
    }
}