Septoku

I first attended the Gathering 4 Gardner (aka G4G) in 2006, via an invitation from my friend Thane Plambeck. One of the G4G traditions is a gift exchange. You produce N copies of a G4G appropriate gift (usually around 300) and bring them to the conference. Then you (eventually) get a bag with N different items from all the exchange participants. It’s good nerdy fun.

This G4G was the seventh one, so the theme was the number 7. I invented a variant of Sudoku on a hex grid that used 7 symbols. I wrote it up with some examples and a few questions (about what solutions looked like, etc). The paper was included in the G4G7 exchange book (buy it here!). A few folks sent me commentary and proofs regarding the puzzle.

A couple years later George Bell did some analysis of septoku and completely demolished it. He found that there is only 6 possible solutions, along with a bunch of other constraints that severely limited its interest as a puzzle.

I’ve archived my original paper along with papers from George and others:

• Septoku From G4G7
• George Bell’s “The mathematics of Septoku” (also on arXiv)
• George Bell’s “Seven Septoku Theorems”
• David Nixon’s Centers Proof
• Amit Khetan and David Moulton’s Corners Proof