[Math] ODE introduction textbook

book-recommendationordinary differential equationsreference-request

Unfortunately I have reached the maximum number of math classes I can take for my undergraduate degree. I still wish to study basic ODEs and basic number theory. What is a good textbook with an introduction to these? I would prefer a textbook that is not super rigorous or formal since I will be studying it on my own time.
Thank you.

Best Answer

I think these two are quite good:

Elementary Differential Equations with Boundary Value Problems (Edwards &Penney)

An Introduction to the Theory of Numbers (G Hardy)