I would just like to respond to Flavio's review. As a physicist, I drew the same kinds of mathematical conclusions he did when he read the book. I do not, however, feel that this is the point. Whether 9 comes out in the decimal system or 7 comes out in the octal system is irrelevant. "No 9" remains a beautifully written piece of literature that expresses author's fascination with numbers and geometry. Sure, you can find rigourous mathematical proofs why '9' must come out. I have worked it out myself, and I don't disagree. However, there are many scientific phenomena (rainbows, fractals etc.) that are no less beautiful despite being taken apart, analysed, and understood.Number 9 is a captivating, well written and beautiful book that was a pleasure to read. The reader is drawn in by the author's fascination with the subject, and kept there by the author's storytelling skill.I recommend it.