[xenotux]

I don't think there's anything that would put some new, esoteric math concept in your mailbox every week, although there's plenty of books that cover recreational mathematics in an accessible way (Martin Gardner, Ian Stewart, etc). And for QM articles, I recommend searching the web - you can often find better explanations on some 1999-style blog somewhere.

The problem with this particular article is simple: busy beavers numbers aren't interesting because they're big. They don't break mathematics because of that; you can always say "+1" to get a larger number. There's also nothing particularly notable about Knuth's up-arrow notation, which is essentially a novelty that you're never gonna use. Instead, the numbers are interesting because they have fairly mind-blowing interactions with the theory of computability.