With the extra constraints in this Sudoku variant, there can't be many unique solutions -- otherwise two numbers wouldn't be sufficient to uniquely specify a so

With the extra constraints in this Sudoku variant, there can't be many unique solutions -- otherwise two numbers wouldn't be sufficient to uniquely specify a solution. In fact, there's only a single pattern. Note how along one axis every digit is 4 higher (mod 9) than the previous digit. One starting digit specifies the starting point (alignment of the pattern), the other starting digit the rotation + mirroring of the pattern. 9 possible alignments times 4 rotations times 2 (mirrored or not) = 9 * 4 * 2 = the 72 different solutions mentioned in the article. But this is caused by the Knight's+King's move constraints (with the "consecutive numbers" constraint prohibiting relabeling of the numbers). There's way more solutions without those extra constraints.