# Knuth reward check

**Knuth reward checks** are checks or check-like certificates awarded by computer scientist Donald Knuth for finding technical, typographical, or historical errors, or making substantial suggestions for his publications. The *MIT Technology Review* describes the checks as "among computerdom's most prized trophies".^{[1]}

## History[edit]

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.^{[2]} 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.^{[3]} By March 2005^{[update]}, the total value of the checks signed by Knuth was over $20,000.^{[4]} Very few of these checks were actually cashed, even the largest ones. More often they have been framed and kept as "bragging rights".^{[5]}^{[6]}

Intelligence: Finding an error in a Knuth text. Stupidity: Cashing that $2.56 check you got.

## Amount[edit]

In the preface of each of his books and on his website,^{[8]} 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.^{[9]} "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.^{[10]} It started at $2.56,^{[3]} and doubled every year until it reached $327.68.^{[3]} Recipients of this "sweepstakes" reward include Chris Thompson (Cambridge) and Bogusław L. Jackowski (Gdańsk),^{[11]} and also Peter Breitenlohner on 20 March 1995.^{[12]}

Each check's memo field identifies the book and page number. 1.23 indicates an error on page 23 of Volume 1. (1.23) indicates a valuable suggestion on that page. The symbol Θ denotes the book *Things a Computer Scientist Rarely Talks About*, KLR denotes the book *Mathematical Writing* (by Knuth, Larrabee, and Roberts), GKP and CM denote the book *Concrete Mathematics* (by Graham, Knuth, and Patashnik), f1 denotes fascicle 1, CMT denotes the book *Computer Modern Typefaces*, DT denotes the book *Digital Typography*, SN denotes *Surreal Numbers*, CWEB denotes the book *The CWEB System of Structured Documentation*, DA denotes the book *Selected Papers on Design of Algorithms*, FG denotes the book *Selected Papers on Fun and Games*, and MM denotes the book *MMIXware - A RISC Computer for the Third Millennium*.

## Delays[edit]

Knuth is often unable to answer immediately when a reader finds a mistake in one of his books or programs. In some cases, the delay has been several years. For example, on 1 July 1996, Knuth sent out more than 250 letters, 125 of which contained checks, for errors reported in *The Art of Computer Programming* since the summer of 1981. A few of these remain unclaimed as of May 2006.^{[13]} When Knuth is not able to reply immediately, he adds 5% interest, compounded continuously, to the reward.^{[14]}

## See also[edit]

## References[edit]

**^**Ditlea, S., "Rewriting the Bible in 0's and 1's",*MIT Technology Review*.**^**http://www-cs-faculty.stanford.edu/~knuth/boss.html.- ^
^{a}^{b}^{c}Donald Knuth (2002), "All questions answered",*Notices of the AMS*49(3): 318-324. **^**NPR Interview.**^**Kara Platoni, "Love at First Byte Archived 2006-06-04 at the Wayback Machine",*Stanford Magazine*, May–June 2006**^**The History of TeX**^**Quotes About Programming**^**See Books in Print by Donald E. Knuth Archived 2006-09-01 at the Wayback Machine**^**Frequently Asked Questions Archived 2012-02-10 at the Wayback Machine on Don Knuth's webpage .**^**Weisstein, Eric W. "Wheat and Chessboard Problem".*MathWorld*.**^**Installation of Knuth's 1995 release Archived 2005-11-20 at the Wayback Machine**^**TUG'95: Questions and Answers with Prof. Donald E. Knuth and Ch 34 of*Digital Typography***^**What is your current mailing address? on Don Knuth's website.**^**See King Solomon and Rabbi Ben Ezra’s Evaluations of Pi.

## External links[edit]

- The Bank of San Serriffe
- Interview (RealVideo format) (or Transcript) with Knuth on National Public Radio