Robert's not too happy when a diminutive number devil visits him in a dream--""If you give me some homework in my dream, I'll scream bloody murder! That's child abuse!""--but his opinion changes over the course of a dozen nights, as the devil shows him how to make numbers hop, introduces ""unreasonable,"" ""prima-donna,"" and ""Bonacci"" numbers, draws number triangles with all sorts of marvelous qualities, discusses one, zero, and infinity, and at the end delivers a dinner invitation to Number Heaven (which is also Number Hell), where Robert meets such mathematical eminences as Lord Rustle (as in Bertrand) and Dr. Happy Little (Felix Klein, inventor of the Klein Bottle), then has dessert--pie, of course. Berner adds plenty of full-color cartoon vignettes and charts; the author supplies several additional exercises for readers, and ends with translations of his quirky terminology and a long index of the concepts he so cleverly introduces. A natural follow-up to Norton Juster's The Phantom Tollbooth (1961) and Jon Scieszka's Math Curse (1995), covering more mathematical territory--with less plot--than either, but sharing the same daffy sensibility.