Although most people wouldn’t think that a book about a number would be interesting, the following shows that’s not always true:

The Golden Ratio: The Story of Phi, the World’s Most Astonishing Number by Mario Livio (Broadway Books, 2003; ISBN: 0767908163)—A history of the number phi (1.6180339887), also known as the golden ratio or divine proportion. There are examples from nature, as well as phi’s use in architecture and art throughout human history.

Pi: A Biography of the World’s Most Mysterious Number by Alfred S. Posamentier and Ingmar Lehmann (Prometheus Books, 2004; ISBN: 1591022002)—The story of the number pi throughout history, from the Old Testament to modern politics. An epilogue has pi expressed to 100,000 decimal places.

e: The Story of a Number by Eli Major (Princeton University Press, 2009; ISBN: 9780691141343). In this new edition of his book, Major traces “e” from the 16th century to the present, winding his story around the properties of this well-known number.

Zero: The Biography of a Dangerous Idea by Charles Seife and Matt Zimet (Penguin Books, 2000; ISBN: 0140296476)—An entertaining story about (literally) nothing. The development and use of nothing, or zero, is covered in detail from ancient times to the present.

An Imaginary Tale: The Story of [the Square Root of Minus One] by Paul Nahin (Princeton University Press, 2010; ISBN: 9780691146003). This instructive book will take the reader through not only the history of complex numbers, but why such imaginary numbers are important to mathematics.

And a book about the importance of all numbers:

Cosmic Numbers: The Numbers that Define Our Universe by James D. Stein (Basic Books, 2011; ISBN: 0465021980). This book traces the power of numbers, noting the “discovery, evolution, and interrelationship of figures that define our world.” In other words, it gives the reader a good reason why numbers are so important to everyone.