See also the small variant based on sums - click here
or on MiniSum above.
In standard Sudokus
one aims to place digits 1 to 9 in each small square so rows, columns and 3x3 mini-arrays
(surrounded by bold lines) contain each digit once.
puzzles (as here), it is also
required that each of the main diagonals contains each digit once. A 'correct'
Sudoku-X will only soluble if use is made of the additional diagonal requirements (i.e. you can't
fill it in fully if you treat it like a standard Sudoku).
page lists collections of both types of puzzles.
page offers a free Windows-compatible Player program for Sudoku/-X
puzzles, as well as downloads of the puzzles featured here.
I also set Killer Sudoku
(which, despite the name, are not necessarily difficult!). These involve Sudoku grids in
which no squares are pre-filled in but in which meshes are used to surround given areas, the
sum of all contained square values being indicated.