A SudokuPX grid has all of the properties of a SudokuP grid, plus diffent values along both diagonals.
I counted these some time ago, but never got around to posting the results.
These grids have far fewer PX-preserving transformations (morph options), in fact as far as I can tell we are reduced to the normal dihedral symmetries, namely transpose and rotation, so there are only 8 morph flavours, none of any interest. Perhaps blue can uncover some!
- there are 133,747,300 different SudokuPX grids (up to relabelling the digits)
- for PX-equivalence under the 8 PX-preserving transformations, we simply enumerated them explicitly and determined the number of PX-different grids as 16,724,358
- for S-equivalence, ie essentially different in the normal Sudoku-equivalence sense, we don't really know. I will leave the ED count calculation as an exercise for Serg
The main question here is the minimum number of clues. We know 12-clue puzzles have been found for SudokuX so the chances are good that we'll find 10-clue, maybe even 8-clue SudokuPX puzzles.
Given the low numbers of grids involved, and that my HS engine is currently in pieces on the garage floor, I invite blue and champagne to perhaps provide an answer to this question.