The book Music and Mathematics is a bit of a jumble of essays from various people. It's not a coherent whole or anything, BUT, if you are the least bit interested in this subject I would strongly you recommend reading the first essay (i.e. chapter). A lot of "music theory" mumbles around circles of fifths and chord progressing and things with vague pretenses of being math, but that chapter includes the only fundamental mathematical idea in the entire book.

Conveniently that chapter, and some others, are here.