Q:

Source material to study number theory?

I don't know if this is the correct site to ask this question, but I felt it was off-topic on the Mathematics forum. I really like Number Theory and would like study some on my own. Which books should I read to get a good grasp on the subject?
I'm a 20 year old Software Engineering student. I've taken courses on introduction to Discrete Math, Linear Algebra, and Calculus I. I'm taking Calculus II and Graph Theory now. My Calculus lacks analysis of series/indefinite integrals though.
As for ability I wouldn't know how to answer. I've aced all those math subjects but they were fairly basic, they're designed for an engineering course after all. They're mostly introductions to the subjects

A:

I've heard very good reviews of the 2017 book, "An Illustrated Theory of Numbers" by MH Weissman.
The book's main site is here; a write-up, along with some reviews, by the American Mathematical Society can be found here. To quote from the latter (emphasis added by me):

An Illustrated Theory of Numbers gives a comprehensive introduction to number theory, with complete proofs, worked examples, and exercises. Its exposition reflects the most recent scholarship in mathematics and its history.
Almost 500 sharp illustrations accompany elegant proofs, from prime decomposition through quadratic reciprocity. Geometric and dynamical arguments provide new insights, and allow for a rigorous approach with less algebraic manipulation. The final chapters contain an extended treatment of binary quadratic forms, using Conway's topograph to solve quadratic Diophantine equations (e.g., Pell's equation) and to study reduction and the finiteness of class numbers.
Data visualizations introduce the reader to open questions and cutting-edge results in analytic number theory such as the Riemann hypothesis, boundedness of prime gaps, and the class number 1 problem. Accompanying each chapter, historical notes curate primary sources and secondary scholarship to trace the development of number theory within and outside the Western tradition.
Requiring only high school algebra and geometry, this text is recommended for a first course in elementary number theory. It is also suitable for mathematicians seeking a fresh perspective on an ancient subject.

