* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
- Add more doctests and type checking to make sure only natural
numbers are used
- Simplified the algorithm slightly
This new verison is also between 10-15% faster for really
long sequences