Consider the question Big O exponential: proving NP is a subset
Asymptotic notation questions have been pretty standard for Stack Overflow. This fairly interesting beginner question is up, but has already accumulated a couple of 'close' votes. One of them is for 'off topic' but, possibly because I'm a theory guy, it seems very much on topic for programming and related topics.
You could argue for "computer science" potentially, but it would seem this, like questions on, oh, NP-complete problems and such, are things serious professional programmers should know and are interested in.
You could also make a case for mathematics and event the theory stack, although it's probably a little light for theory. But with all of these separate categories, there seems to me to be a real risk that interesting questions will be modded/closed/moved until the OP loses interest.
Perhaps we've gotten a little too compartmentalized?