How to find all perfect numbers in specific interval in c++?

Question

I want to find all perfect numbers from interval x to y. Any help how can I do that ?

score 3 · Accepted Answer · answered Nov 05 '13 at 17:51

3

Here is a simple solution, it's not very fast, just an example to understand how perfect numbers work.

#include <iostream>

using namespace std;

int main()
{
    int x, y;
    int sum_del;
    cin >> x >> y;
    for(int i = x; i <= y; i++){

        sum_del = 0;

        for (int j = 1; j <= i/2; j++){
            if (i % j == 0)
                sum_del += j;
        }

        if (sum_del == i)
            cout << i << endl;

    }
    return 0;
}

answered Nov 05 '13 at 17:51

user2699298

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1

There's also no need to check until i/2, it's enough to go from 2 to sqrt(i). :) – Eutherpy Nov 05 '13 at 17:54
thanks, i get it. thanks for the example! – user2943407 Nov 05 '13 at 18:02
Actually, the best thing to do would be to skip every second (every odd) number - there's a theorem proving that, if there is an odd perfect number, it has to be greater than 10^300. – Eutherpy Nov 05 '13 at 18:04

How to find all perfect numbers in specific interval in c++?

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