(No, it’s not Sudoku.)
After a many-year hiatus, I just re-subscribed to GAMES Magazine, and in my first issue (September 2009), I was pleased to discover several puzzles with a mathematical slant. One of them was Strimko, a puzzle based on Latin squares, and developed by the Grabarchuk family. Here’s an example (click to solve online):
The idea is simple: each row and column of an nxn grid must contain the number 1, 2, …, n exactly once (that is, the grid must form a Latin square), and each “stream” (connected path in the grid) must also contain the numbers 1, 2, …, n exactly once.
The official site claims that the minimum number of clues required for an nxn grid is n-1 for n=4, 5, 6, and 7, and also says, “This is another unique feature of Strimko.” They do not provide a proof, though, so here’s an opportunity for a nice exercise. (On a related note, a MathSciNet search for “Strimko” returned 0 results, while “latin square” returned 1888 results. It is left to the reader to determine if there’s anything relevant there.)
There are a few sites that provide weekly (here) or monthly (here, here) puzzle sets. So in addition to your daily Sudoku fix, maybe a crossword puzzle, and checking your email, you now have yet another way to avoid doing work.