With a title like Honorary Senior Research Fellow at the Department of Computer Science, University College London," one would expect Peter J. Bentley's work to be quite good. Dr. Bentley's bio on his website clearly communicates that this is a man who is quite intelligent. His work outside of writing is a strong indicator that he is a cut or two above the norm.
As such, there is no excuse for some of the outright errors in his writing. Trivial errors that a first year math major knows to avoid.
When discussing prime and composite numbers, Dr. Bentley uses the number 72 to illustrate how any number that is not prime can be broken down into a product of prime factors. He states that 72 = 4 * 18, and 18 = 2 * 9 and 4 = 2 * 2. Thus the factors are 2 * 2 * 2 * 9. "And, you guessed it, both 9 and 2 are prime numbers." Call me crazy, but 9 is not a prime number. It is a composite of 3 * 3, where 3 IS prime. A mistake like this is utter carelessness.
The next paragraph leaves no time for respite. When speaking of how Euclid proved this concept he states "He didn't just hope that his theorem was true. If he relied on hope, we'd still be calling it a ---theory.---" The mathematical word Dr. Bentley was looking for here is "Conjecture." A theory is a well-substantiated explanation of some aspect of the natural world. By saying something would be a theory if it was unsubstantiated, he propogates a continuing myth about science and knowledge.
And Dr. Bentley does not seem the type to want to promote that area of misunderstanding. In fact, much of his writing intimates a strong bias against religious belief and persons (The people who so often claim that evolution is "just a theory"). Following his incorrect statement about theories, he provides an example of proof by contradiction. Within the example, he uses The Flying Spaghetti Monster (FSM) as the moving force of the proof. The FSM is a well-known parody religion used (and created) to make fun of Intelligent Design and Christianity. His bias continues when he's speaking of irrational numbers and the Pythagoreans. He states that when they realized irrational numbers conflicted with their religious beliefs they "did what any good religious sect does and suppressed the truth." Such a blanketing statement is an unpardonable logical fallacy. Bias and beliefs are an aspect of who we are, but they have no business being in a popular science book about numbers.
I have been using The Book of Numbers as my bathroom reader for a while now. Previously, I have found the information to be fascinating and enjoyable. Now, however, after stumbling across blatant errors in quick succession, I find myself more concerned about the truth value of Dr. Bentley's statements than about actually reading the book. As a senior research fellow, and an obviously brilliant man, he should know better.