GCD Rokudoku
To go along with the previous Quadrata puzzle which involved the LCM of adjacent entries, here are some GCD puzzles I made this morning.
An issue with making greatest common divisor puzzles on the nine-by-nine board is that the numbers 1,5, and 7 are indistinguishable, as when combined with any other number in our range we always get 1. Another problem arises from 4 and 8 which have a GCD of 4. These give a 2 when paired with any even and a 1 when paired with any odd, so they're indistinguishable from each other as well.
Things get a little simpler when we trim down to the six-by-six case, where 1 and 5, and 2 and 4 are the only trouble-making partnerships. We can fix that issue by simply forcing certain cells to be below 3, which is what we do here.
As shidoku is the common term for four-by-four caged puzzles, I use the word for six and call this a rokudoku. For more info on sudoku terminology click here.
The first one is done for you to give you a quick idea of how things work. The puzzles get harder as they go, the last being rather tricky. Look further below for a higher quality PDF, the solution, and separate copies of the three puzzles for those who want larger squares.
Single page versions:
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