While being on the vacations I found an excellent popular math book, probably the best book in its genre: Prime Obsession by John Derbyshire.
This book tells about one of the greatest and deepest mathematical problems: The Riemann Hypothesis.
One of the best qualities of this book is its style – you don’t need to be a professional mathematician to understand that, especially to understand depth and beauty of this problem (which seem to me overly complex when I first seen it a few years ago, out of pure interest).
The book also briefly introduces all the required mathematical basis to understand the hypothesis and the related things. It does so in brief but understandable manner, even quite a complex mathematical concepts as operator theory and theory of functions of a complex variable are given in elegant and understandable manner. You don’t need to be a professional mathematician to understand that yet you will be able to verify the formulas and theorems given in the book by yourself and find that the mathematics beyond that hypothesis is beautiful beyond words. It is amazing to see how seemingly disparate mathematical branches as math analysis, complex numbers, matrix stuff, number theory and even quantum mechanics are related to this problem and discover its fantastic depth.
Unlike most of the ordinary fictional and popular books you can return to this one again and again since it is very deep and versatile.
Hope you’ll enjoy it as I did