This is a text that defines "the number of ways there are of doing some well-defined operation." Covers permutations and combinations associated with elementary algebra, generating functions, the principle of inclusion and exclusion, the cycles of permutations, the theory of distributions, partitions, compositions, trees, and linear graphs; and permutations with restricted position. Includes problems. 1958 edition.
This was explicitly recommended by Cyril Domb in "Domb and Green" in volume 3 of Phase Transitions and Critical Phenomena.
I'm not quite smart enough to hold everything in my head all at once, but certainly one hell of a ride. By the time you get to the Cayley trees you feel like you are swimming through cement, every line charged with meaning. That's what actual learning feels like I suppose, a not entirely pleasant burn. You don't get stronger lifting cans of tunafish.