Few years back, some people used to write “Kenneth Rosen” for these type of questions but now-a-days I rarely see it here.

You can read the following books to understand generating function or to understand the discrete mathematics as a subject:

- Discrete Mathematics and Its Applications by Kenneth H. Rosen
- Concrete Mathematics by Graham, Knuth and Patashnik
- Discrete and Combinatorial Mathematics by Ralph P. Grimaldi