prime_gaps.cpp

#include <iostream>
#include <cmath>
#include <string>
#include <iomanip>

bool prime(unsigned long long n) {
    if (n <= 1) return false;
    if (n <= 3) return true;
    if (n % 2 == 0 || n % 3 == 0) return false;
    
    for (unsigned long long i = 5; i * i <= n; i += 6) {
        if (n % i == 0 || n % (i + 2) == 0) return false;
    }
    return true;
}

std::string centerString(unsigned long long num, int width) {
    std::string numStr = std::to_string(num);
    int padding = width - numStr.length();
    int leftPad = padding / 2;
    int rightPad = padding - leftPad;
    return std::string(leftPad, ' ') + numStr + std::string(rightPad, ' ');
}

int main() {
    unsigned long long a = 10e6; // Can be increased to a much larger value now
    unsigned long long diff = 0;
    unsigned long long prev = 2;
    int gap = 11;
    
    for (unsigned long long i = 3; i <= a; i++) {
        if (prime(i)) {
            unsigned long long k = i - prev;
            unsigned long long pd = diff;
            
            if (k > diff) {
                std::cout << centerString(i, gap) << "-" << centerString(prev, gap) << " = " << i - prev << std::endl;
            }
            diff = std::max(diff, k);
            prev = i;
        }
        
        std::cout << i << '\r' << std::flush;
        double l = log10(static_cast<double>(i));
        if (l == static_cast<int>(l)) {
            std::cout << std::string(33, '-') << std::endl;
            std::cout << "\nMax diff till 10e" << static_cast<int>(l) << ": " << diff << "\n" << std::endl;
        }
    }
    
    return 0;
}