If you inclined towards mathematics, but almost didn’t touch it since college years and want to get a math rush again, then following are the books that you may find captivating.
I should mention that these are books on Applied Mathematics which is of useful kind paraphrasing Richard Feynman. The books are ordered from easy to not so.
1. Applied Mathematics: A Very Short Introduction by Alain Goriely. This book is a gentle intro to applied math and Alain is capable of explaining things lucidly and as simple as required, but not too much.
2. Street-Fighting Mathematics:
The Art of Educated Guessing and Opportunistic Problem Solving by Sanjoy Mahajan is more involved and requires some work on readers part, but it’s a delight to read. This book is available in open access here.
3. Next book from the same author is The Art of Insight in Science and Engineering: Mastering Complexity. It is somewhat similar to the former, but different. Again it’s open for public
4. Now, the last one is a real textbook on Applied Mathematics by J. David Logan, but nevertheless it is interesting to read and work through.