CGCPNG:2008 /barcode.zip .png
Trivia: Despite the comments on the game page, this was a title written specially for the CSSCGC in 2008, on the Spectrum. The ZX81 "original" was in fact a quick back-port of the Spectrum version. It is, indeed, impossible to lose due to the number of of numbers able to be chosen from, and the amount of guesses allowed. Choosing the same number multiple times is blocked by the game, rather than being counted as an incorrect guess.