I brought this home from the thrift store, without any particularly high hopes for getting Dollygirl interested in a story that was supposed to be a mathematical version of The Phantom Tollbooth or Alice in Wonderland. Such books often have a didactic smell of the nursery, even when they're new; and this one is fairly new: it was published in German in 1999, and the English translation came out in 2000. And translated books...well, sometimes they work and sometimes they don't. I am very happy to say that The Number Devil (at least the ten of twelve chapters we've read) has surpassed not only my expectations, but Dollygirl's.
I like the fact that several of the math threads continue throughout the book, such as "Bonacci numbers" (what the Number Devil calls the Fibonacci sequence). I've seen too many books that give a page or so to things like that, and then it's off to something completely different and you never see them again. Robert's dreams have different topics, but they're definitely sequential...and they come back to a starting place, usually "one." (Who knew that "one" could be so interesting?) I also like the colourful diagrams; to my poor non-math-major's mind, they make some kind of sense. The dialogue is snappy, not patronizing, and doesn't get bogged down with what it's trying to teach; that in itself is worth a few stars.
We'll miss the Number Devil when the dreams are over.
Highly recommended, probably best for ages 10-14.