This adds two things over the OP's initial version, both mentioned in the post: wheel factorization (with 30), and the "linear probing" to avoid lists. It's pos

This adds two things over the OP's initial version, both mentioned in the post: wheel factorization (with 30), and the "linear probing" to avoid lists. It's possible to keep improving (up to a point) by using e.g. wheel with 210 instead of 30, and so on, if one doesn't mind hard-coding more and more.