I graduated at engineering and I know a fair amount of real analysis, calculus, etc. I read Apostol's book on analytic number theory.
I'm looking for some book to see a bit more about the theory on studying whether a number is o isn't rational. I'm not sure where to look though. I thought about p-adic theory, groups, rings, etc. And it made more confused.
Can you guys recommend me some material to study this area of math?
Try Ed Burger, Exploring the Number Jungle, and Making Transcendence Transparent.