Knuth reward check
Knuth reward checks are checks or check-like certificates awarded by computer scientist Donald Knuth for finding mathematical errors, or making substantial suggestions for his publications. The MIT Technology Review describes the checks as "among computerdom's most prized trophies".
Initially, Knuth sent real, negotiable checks to recipients. He stopped doing so in October 2008 because of problems with check fraud. As a replacement, he started his own "Bank of San Serriffe", in the fictional nation of San Serriffe, which keeps an account for everyone who found an error since 2006. Knuth now sends out "hexadecimal certificates" instead of negotiable checks.
As of October 2001[update], Knuth reported having written more than 2,000 checks, with an average value exceeding $8 per check. By March 2005[update], the total value of the checks signed by Knuth was over $20,000. Very few of these checks were actually cashed, even the largest ones. More often they have been framed and kept as "bragging rights".
In the preface of each of his books and on his website, Knuth offers a reward of $2.56 (USD) to the first person to find each error in his published books, whether it be technical, typographical, or historical. Knuth explains that $2.56, or 256 cents, corresponds to one hexadecimal dollar. "Valuable suggestions" are worth 32 cents, or about 1⁄8 of the errors in the book (0.2 hexadecimal dollars or 20 hexadecimal cents). In his earlier books a smaller reward was offered. For example, the 2nd edition of The Art of Computer Programming, Volume 1, offered $2.00.
The reward for coding errors found in Knuth's TeX and Metafont programs (as distinguished from errors in Knuth's books) followed an audacious scheme inspired by the Wheat and Chessboard Problem. It started at $2.56, and doubled every year until it reached $327.68. Recipients of this "sweepstakes" reward include Chris Thompson (Cambridge) and (Gdańsk), and also Peter Breitenlohner on 20 March 1995.
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