Kenneth H. Rosen

Discrete Mathematics and Its Applications is a decent beginner discrete mathematics textbook that doubles as a beginner logic book (shockingly). The beginning pages of the textbook could be faster paced, though it is better a textbook be slow and elaborate than fast and incomprehensible. High-school level, it is a very easy book and could be completed in under a week.

I used this textbook in my undergraduate discrete mathematics course. I majored in astrophysics and mathematics, so most of my courses were challenging; however, discrete mathematics was extremely easy. The content was obvious enough that I didn't really need a textbook to explain it.

This book is designed as a text for an undergraduate number theory course at any level. The Cryptography is the key.