Good suggestions, and thanks. Yes, I left the area vague. There are a lot of things I'd like to brush up on, so I guess this is vague.

Back to books is a good suggestion. I've been reading Mathematics for the Mathematician and it's fun, but... really eurocentric and sexist. (Yeah, you don't associate that with a book on math do you? Well, it is.) I don't think a book like this would be published today.

Videos, also a good suggestion.

Also now that I know how to use emacs calc, I can do a lot of math fast, I just don't know how it works.