I liked Concrete Mathematics by Ron Graham, Donald Knuth, and Oren Patashnik. Get it from the library of a nearby university, read the first chapter, do the war

I liked Concrete Mathematics by Ron Graham, Donald Knuth, and Oren Patashnik. Get it from the library of a nearby university, read the first chapter, do the warm-up problems, then decide if you like it enough to read the rest. The authors have a way of digging deeper into problems than you might expect. It's not a book where you learn some theorems, then apply them in the problems.