Sudoku is short for "the digits must be single". I wondered if inverting this would work: "the digits must be repeated". And so, by swapping "doku" for "fuku", Sufuku was born.

In short, instead of using numbers 1-9 for a 9x9 board, you use 2 twice, 3 three times, and 4 four times (for a total of 9).

It plays differently from sudoku than I expected. I assumed it would be simpler, since you have fewer digits. But once I settled on irregular region shapes, I discovered that it can also be quite difficult. In sudoku you eliminate a number by placing it; in sufuku a number is only eliminated once all its copies are placed. So you count lines instead of mostly scanning the board.

As I want the game to be approachable, the daily boards are mostly 6x6 or 7x7 for now. Larger boards are more interesting because 6x6 has only one set of numbers: [1, 2, 3]. But for 9x9 you can go with [2, 3, 4], [1, 3, 5], or [1, 2, 6] (I skip pairs like [2, 7] because I consider them boring). 10x10 is the first one that offers a set of four numbers: [1, 2, 3, 4].

Of course it turns out the idea has been around for some time: 2-3-4 Sudoku (Uwe Wiedemann) and Sudoku Ripeto (Miguel Palomo). I'm curious what you make of it as a daily game.

Today's Friday, so the board is on the harder side. You can play easier boards in this week's archive.