Mark's earlier post [1] which covered divisibility much more extensively mentioned a division algorithm that I've never learned: short division.

Also, that earlier post introduces a graph-/regex-/dfa-based solution for solving divisibility that reminds me of [2].

[1]: https://blog.plover.com/math/divisibility-by-7.html

[2]: https://codegolf.stackexchange.com/a/75326