Classic Mathematics Books for Lifelong Learners

Concrete mathematics is great but not something you could suggest to, for example, a biologist or medical doctor that wants a deeper understanding of some aspect of mathematics. It's (explicitly) meant for computer science.

In a similar vein, I love documentaries and I learned much as a child that way. I find that they are way too basic now and often repeat things I've seen/known for years. This is needed for other kids of course, but as an adult the only stuff is really basic or so advanced that it is actual work to make it through (tough after a rough week at work).

One of my favorite examples of finding the middle ground is in dealing with SETI. I love the subject and have seen numerous documentaries on it over the years that cover what they're doing from 50,000 feet. Paul Davies is the lead at SETI and I read his book "The Eerie Silence" and it was really awesome. It perfectly found the middle ground between a documentary which has to be ok for children and a textbook on the subject. Paul Davies is kind of to SETI what Alan Kay is to computing in some ways as someone with deep experience in the field and lots of philosophical thoughts on the subject. His writing is really clear though (I love Kay, but don't have a strong enough computing, historical computing, math, or biology background to keep up with a lot of his writing). Two others that stand out to me are the classic "A Brief History of Time" by Stephen Hawking that blew my mind as a kid and the equally good, but lesser known "Black Holes and Time Warps" by Kip Thorne which made an excellent follow up book that gives a good high level appreciation which would likely be helpful for anyone planning to study those subjects in college at a rigorous mathematical level. Kip's book is also funny. There is a picture of Stephen Hawking delivering him a years subscription to a magazine (I think it might have been lewd in nature) for losing a bet to Kip over whether Cygnus A would have a black hole I think. As a highschool student I wrote to him with some career questions and he was kind enough to respond! Max Tegmark has a book "Our Mathematical Universe" which covers two parts: one on why we might be part of a simulation, and the first part which is like a condensed cosmology lesson from A to Z. He had a big part in several big discoveries and hearing the play by play is gripping. He was apparently a pretty gifted coder, so he got tasked with a lot of the data analysis and therefore he and his first wife were among the first to see the actual results of these big experiments. Code by Petzold is also an amazing tour de force if you want to understand computers.