But while there are many difficult for human comprehension packing constraints within non-consecutive puzzles, these strong constraints offer the possibility, with careful construction/testing, for cool missing digit themes, like using just even numbers as I did in Mutant Sudoku and which I saw again on the excellent May Sudoku test on LMI. I'd found (easily by computer, impossible by actual solving) a one-digit/six clue NC awhile ago. It's not worth playing with but this is certainly the unique solution. My experiment this week was to do something a little more possible - a two-digit NC - that could actually be solved. This one worked out perfectly for my expectations (with at least one nice non-standard elimination on my pathway). The only sacrifice was symmetry to get some of the givens in solver-friendly places. Please enjoy.
Rules: Place a single digit from 1 to 9 into each cell so that no digit repeats in any row, column, or 3x3 region. Consecutive digits (ie 3 and 4) cannot be placed in vertically or horizontally adjacent cells.