I'm trying to find what the formula is for the number of possible variations to this puzzle. I know that there is only one answer (or 4, when taking into account the variations when the grid is flipped on either axis). Does a formula exist to describe the number of combinations/permutations here? One that could be applied if the rules of the puzzle were changed? (ie, if preceding/following numbers could be placed diagonally to each other, but still not vertically or horizontally, how many possible combinations/permutations would there be?
Correct me if I'm wrong, but the way I'm looking at it, the number of possible permutations when it comes to the original problem is 1, and the number of possible combinations is 4.
Perhaps I'm looking in completely the wrong direction?