Reddit mentions of A Friendly Introduction to Number Theory (4th Edition)

Quantum Computing Since Democritus by Scott Aaronson.

A Friendly Introduction to Number Theory by Silverman.

Visual Complex Analysis by Needham.

Sounds like what you want is elementary number theory, which fortunately is something you can get in to without any real prerequisites.

There are some decent textbook recommendations here that you could try out (although as a warning, not all of those are for elementary number theory, check the descriptions). Perhaps Silverman's book would be a good one to try out, though there are certainly lots of other options if you'd rather try a different one. [Edit:Looks like velcrorex suggested the exact same book. I've definitely heard good things about it.]

Fermat's little theorem, Euler's theorem, Euclid's algorithm for greatest common denominators (specifically Euclid's extended algorithm to generate multiplicative inverses), Carmichael numbers, Fermat primality test, Miller-Rabin primality test, modular exponentiation, and discrete logarithms.

If you want to go further you may want to learn about things like finite fields (specifically Galois fields), polynomial rings, elliptic curves, etc. This isn't meant to limit things; e.g., cryptography (and attacks on cryptography) aren't necessarily limited to these types of math. E.g., NUTRUEncrypt is based on lattices/shortest vector problem, and the McEliece Cryptosystem is based on Goppa codes, but again you still need to learn the math above to be able to understand this math.

http://www.amazon.com/Friendly-Introduction-Number-Theory-Featured/dp/0321816196/ref=sr_1_1?ie=UTF8&qid=1425696135&sr=8-1&keywords=A+Friendly+Introduction+to+Number+Theory+%284th+Edition%29+%28Featured+Titles+for+Number+Theory%29

Try these books(the authors will hold your hand tight while walking you through interesting math landscapes):

Discrete Mathematics with Applications by Susanna Epp

Learning to Reason: An Introduction to Logic, Sets, and Relations by Nancy Rodgers

A Friendly Introduction to Number Theory Joseph Silverman

A First Course in Mathematical Analysis by David Brannan

The Foundations of Analysis: A Straightforward Introduction: Book 1 Logic, Sets and Numbers by K. G. Binmore

The Foundations of Topological Analysis: A Straightforward Introduction: Book 2 Topological Ideas by K. G. Binmore

Introductory Modern Algebra: A Historical Approach by Saul Stahl


An Introduction to Abstract Algebra VOLUME 1(very elementary)
by F. M. Hall

There is a wealth of phenomenally well-written books and as many books written by people who have no business writing math books. Also, Dover books are, as cheap as they are, usually hit or miss.

One more thing:

Suppose your chosen author sets the goal of learning a, b, c, d. Expect to be told about a and possibly c explicitly. You're expected to figure out b and d on your own. The books listed above are an exception, but still be prepared to work your ass off.

For compsci you need to study tons and tons and tons of discrete math. That means you don't need much of analysis business(too continuous). Instead you want to study combinatorics, graph theory, number theory, abstract algebra and the like.

Intro to math language(several of several million existing books on the topic). You want to study several books because what's overlooked by one author will be covered by another:

Discrete Mathematics with Applications by Susanna Epp

Mathematical Proofs: A Transition to Advanced Mathematics by Gary Chartrand, Albert D. Polimeni, Ping Zhang

Learning to Reason: An Introduction to Logic, Sets, and Relations by Nancy Rodgers

Numbers and Proofs by Allenby

Mathematics: A Discrete Introduction by Edward Scheinerman

How to Prove It: A Structured Approach by Daniel Velleman

Theorems, Corollaries, Lemmas, and Methods of Proof by Richard Rossi

Some special topics(elementary treatment):

Rings, Fields and Groups: An Introduction to Abstract Algebra by R. B. J. T. Allenby

A Friendly Introduction to Number Theory Joseph Silverman

Elements of Number Theory by John Stillwell

A Primer in Combinatorics by Kheyfits

Counting by Khee Meng Koh

Combinatorics: A Guided Tour by David Mazur


Just a nice bunch of related books great to have read:

generatingfunctionology by Herbert Wilf

The Concrete Tetrahedron: Symbolic Sums, Recurrence Equations, Generating Functions, Asymptotic Estimates by by Manuel Kauers, Peter Paule

A = B by Marko Petkovsek, Herbert S Wilf, Doron Zeilberger

If you wanna do graphics stuff, you wanna do some applied Linear Algebra:

Linear Algebra by Allenby

Linear Algebra Through Geometry by Thomas Banchoff, John Wermer

Linear Algebra by Richard Bronson, Gabriel B. Costa, John T. Saccoman

Best of Luck.