//very basic, just searches for mersenne primes. unoptimised. works
//praštevila oblike 2^n -1
#include <iostream>
#include <fstream>
#include <cmath> //pow(), sqrt()
using namespace std;

int main()
{
    ofstream out_data("mersenne.txt");
    do {
        unsigned long long int num = 0, max_n;
        bool prime = true;
        cout << "\n\nVpisi max stevilo: ";
        cin >> max_n;

        for (unsigned long long int power = 2; num <= max_n; power++) //loops powers
        {
            num = 1;
            for (int i = 0; i < power; i++)
                num *= 2;
            num--;
            for (unsigned long long int i = 2; (i <= sqrt(num) +1) && (prime == true); i++) //tests if prime
            {
                if (num%i == 0)
                {
                    prime = false;
                    cout << "\nFailed at pow " << power << " since div by " << i; //dej stran na konc, to za debugging
                }
                else
                    prime = true;
            }
            if (prime == true)
            {
                cout << "\nMersenne prastevilo: 2^" << power<< " - 1 = " << num;
                out_data << "2^" << power << "-1 = " << num << endl;
            }
            prime = true;
        }
    } while (true);
    return 0;
}