I like Calculus, Linear Algebra, Number Theory, Geometry, etc. I pretty much like everything about Math. :) The good thing about math is that all you need is a good book, a stack of paper, a pencil and you are good to go! Is there a fun undergraduate textbook you can recommend me to refresh everything? THX!
I think absolutely is this one:
Personally, I consider it is very, very rigorous and reached a very high level mathematically. However, it only requires a good high-school mathematics foundation. So definitely a great choice for fun and serious learning. The exercises in this book is very good as well.