static std::vector<int> factorize(const int N)
{
std::vector<int> factors;
int n = N;
while (n > 1) {
const int n0 = smallest_divisor(n);
factors.push_back(n0);
n /= n0;
}
return factors;
}
bool is_prime(int n) {
return (n == smallest_divisor(n));
}
