Method iterator

less_slow.cpp:3920–3920

        using iterator_concept = std::input_iterator_tag;

        constexpr iterator() = default;
        constexpr iterator(std::uint64_t n) noexcept : number_(n), factor_(2) { advance(); }
        constexpr std::uint64_t operator*() const noexcept { return factor_; }
        constexpr iterator &operator++() noexcept {