One of Charlie Stross' series, the Laundry books, is in the horror genre. Of course, it has a representatively Strossian twist: in that universe, the incantations required to bridge the gap between our world and the Ones Where The Demons Are take the form of mathematics. There are equations that can drive you insane; thoughts that, when you have them, your head becomes a conduit for Evil. It's an extension of the forbidden-knowledge meme, and it has all the standard trappings thereof; when it's well done, that meme drives the horror stories that I find most creepy. And Stross does do it well.
Anyway, the real reason I brought all this up is to show you this image, which demonstrates pretty effectively the idea of black math:
I think I speak for us all when I say that that is probably the best Garfield cartoon I've ever seen.