# many solutions (72 empty cells)
 1 0 0 0 0 0 0 0 0
 0 2 0 0 0 0 0 0 0
 0 0 3 0 0 0 0 0 0
 0 0 0 4 0 0 0 0 0
 0 0 0 0 5 0 0 0 0
 0 0 0 0 0 6 0 0 0
 0 0 0 0 0 0 7 0 0
 0 0 0 0 0 0 0 8 0
 0 0 0 0 0 0 0 0 9