Concrete Mathematics is in fact an elaboration on the chapter covering the prereq in TAOCP. It was well worth it considering how great this chapter is.
The best part of TAOCP for me is how incredibly good the exercises are. The gradual difficulty is perfect and from 20 onwards you always get some interring insight from solving them. I am especially M and HM ones which are amongst some of the best maths problems I have seen despite being in a CS book.
