I might take Number Theory in college just for fun. Is this class easy? I mean, I was told about about this class by one of my teachers, and ever since then, I became interested in it. Is this class fun? Is it easy? Should I take it? Also, where can I find an online book or something if I want to learn Number Theory by myself? Is there a free book online? I found one ebook for number theory, but its not really good, and doesn't explain things clearly.