Although I am a programmer, I highly recommend this book:

https://www.amazon.com/Math-Book-Pythagoras-Milestones-Mathematics/dp/1402788290

Math’s infinite mysteries and beauty unfold in this follow-up to the best-selling The Science Book. Beginning millions of years ago with ancient “ant odometers” and moving through time to our modern-day quest for new dimensions, it covers 250 milestones in mathematical history. Among the numerous delights readers will learn about as they dip into this inviting anthology: cicada-generated prime numbers, magic squares from centuries ago, the discovery of pi and calculus, and the butterfly effect. Each topic gets a lavishly illustrated spread with stunning color art, along with formulas and concepts, fascinating facts about scientists’ lives, and real-world applications of the theorems.

I have a local publisher version with a different book cover and overall design. The book covers fairly complicated topics written in an easy-to-understand style targeting a broad range of readers.

I believe a guy with a Ph.D. in math can enjoy interesting math facts in a relaxing way.