//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");//naredi 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++) //vrti čez n; power na 2 na začetku saj 1 ni praštevilo.
        {
            num = pow(2, power) - 1; //dodeli vrednost 2^n - 1
            for (unsigned long long int i = 2; (i <= sqrt(num) +1) && (prime == true); i++) //testira če je praštevilo
            {
                if (num%i == 0)
                {
                    prime = false;
                    //cout << "\nFailed at pow" << power << "since div by " << i; (this debugs output and tells me everything is fucked up)
                }
                else
                    prime = true;
            }
            if (prime == true)
            {
                cout << "\nMersenne prastevilo: 2^" << power<< " - 1 = " << num;
                out_data << "2^" << power << "-1 = " << num << endl; //zapiše rezultate v mersenne.txt
            }
            prime = true;
        }
    } while (true);
    return 0;
}