The other day I went to my pigeon-hole to collect my snail mail, and I had a letter from Donald E. Knuth, Professor Emeritus of the Art of Computer Programming!
Inside, there was a check for a correction I sent him some months ago. In fact, it was not really a correction; it was more like a comment. And it was so obvious (he even said that) that he just sent $\$$0.32, instead of the usual $\$$2.56. But hey, who cares? I’ve got Knuth’s autograph now
Perhaps I should set as one of my goals to find a proper error, so that I can receive a $\$$2.56 check By the way, the errata of the Concrete Mathematics is available online and this particular omission is documented as follows:
page 338, line 2 from the bottom
change “for $z$” to “for $z$ and multiplying by $a$”