The title refers to happy numbers, which are positive integers with the property that iterating the process of squaring and summing the digits eventually terminates in the number 1. [At least, that is the simplest case. The idea has been generalized in papers by number theorists who consider iterating more general processes on the digits in different bases.] This mathematical idea arises initially in an anecdote about a former teacher who introduced him to the idea, but is effectively (if not also obviously) utilized throughout as a metaphor for a person's happiness. There are also some intriguing mathematical questions posed on a special test that is given to Julius along with other former IMO contestants. Otherwise, the role of mathematics in the story is really to provide us with an understanding of Julius, his anti-social behavior, and his worldview.

International Mathematics Olympiad (IMO). (NB Contrary to what the book claims, the IMO is not a contest for university students representing a particular college but rather for high school students representing a country.)

I am quite tired of the mathematical stereotype portrayed. (I cannot say I have ever met a real mathematician quite like this, though it appears so often in fiction that someone who knows no better should be forgiven for thinking that most mathematicians are like that.) Still, unlike some other works with similar characters, I never really felt like giving up and stayed interested in the plot all the way until the end. Its uniqueness is probably its best feature of this book. In fact, I am having trouble identifying which tags to apply to this work. It is a bit of a murder mystery, in a strange way, and almost but not quite a fantasy. I can honestly say that this is the best book narrated by a drug-addicted transexual "Cupid" that I have ever read!