Knuth reward check

[1] Knuth started rewarding people for discovering errors in his books after he published the first volume of The Art of Computer Programming in 1968.

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] starting at $2.56, and doubling 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.

Knuth is often unable to answer immediately when a reader finds a mistake in one of his books or programs.

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.

One of Donald Knuth's personally-designed reward checks, with the recipient's name and design details censored to deter forgeries
Bank of San Serriffe reward check