Here is the unique numbers list for 6 in a 8 x 8 grid.

012345612
1314151623242526
343536454656123124
125126134135136145146156
234235236245246256345346
356456123412351236124512461256
13451346135614562345234623562456
3456123451234612356124561345623456123456

Total Combinations: 63