Knuth, Donald Ervin Easter Egg - Royalties

Look in the index for Volume 3 "Searching and Sorting" under "Royalties, use of." It will lead you to a page that contains an exercise referring to the notion of an "organ-pipe distribution." This is a reference to the fact that the author used the royalties from this book's predecessor to have a pipe organ installed in his house.

(I didn't find this, and I don't remember who did)