Number Shark

Number Shark is an educational puzzle game bundled with the freeware cryptographic program CrypTool. It is directly based on the educational game Der Zahlenhai by Lothar Carl, itself an adaptation of the Taxman game concept. The player must compete against a "Number Shark" to get a higher score.

In the beginning, there is a number of shells on the board (their number can be adjusted by the player when starting a game), numbered starting from 1. The player removes one of the shells, and receives as many points as the number on the shell says. However, the Number Shark will then take for himself all of the available shells which have numbers that are real factors of the player's chosen number. (For instance, if there are shells with the numbers 2, 6, 8, 9, 16 available, and the player chooses 16, then the shark takes the shells 2 and 8 and gets 10 points.) If there are no such real factors still present on board, the shark instead takes for himself the number that the player has picked (so, if in the above example the player had picked 9 instead, the shark wouldn't be able to find any real factors of this number and would take shell 9 for himself, denying the player any points.) The game continues until all the shells are gone, at which point the player wins if he has accumulated more points.