TITLE: How do I go about doing math as a hobby?
QUESTION [5 upvotes]: want to study math as a hobby. I find it very interesting, but I made a lot of twists and turns in college which lead me on a different path. Plus, I'm not really sure I'm gifted enough to hack it at the grad school level. I have taken Calc one and I have taken applied math classes for my economics major which involve some work with differential equations. I was wondering where I should go from here if I'm interested in Number theory and Combinatorics? I was also wondering how important Calc II and CalcIII are with regards to these areas of mathematics? What lower level maths should I read up on? Linear? Set theory? What books to people recommend? Should I get a tutor, or do you guys think it is conceivable to cover such advanced topics being an autodidact? Any answers would be helpful.
Thanks a bunch!

REPLY [4 votes]: You can start learning combinatorics with what you already have; any undergraduate discrete math text will have at least some of the basics, but I especially like Edward A. Scheinerman, Mathematics: A Discrete Introduction. Going beyond that, there is Miklós Bóna, A Walk Through Combinatorics: An Introduction to Enumeration and Graph Theory. I’ve also heard very good things about Arthur T. Benjamin & Jennifer Quinn, Proofs that Really Count: The Art of Combinatorial Proof. The last one requires a little more mathematical sophistication than the first two, but still not much in the way of technical background.