TITLE: Suggestion regarding transition to Mathematics
QUESTION [5 upvotes]: I have studied mathematics upto High school level and also studied Calculus 1 and 2. I also have studied basic ODE. Recently i read a book "The Heart of Mathematics : Invitation to effective thinking". Now i feel like pursuing mathematics especially number theory area on my own. I would welcome suggestions of experienced mathematicians so as to what should be the pathway to it. Thanks

REPLY [2 votes]: I'm glad you liked "Heart of Mathematics", it's one of my favorite books.
You might try a book like "Elementary Number Theory and Its Applications" by Rosen.  Hardy and Wright, recommended in another reply, is an excellent book, but it's a big jump from "Heart of Mathematics" to Hardy and Wright.  Rosen's book is simpler, and the only prerequisite is high-school algebra.