This work is licensed under a Creative Commons Attribution 4.0 International License. Bob Bosch and Mike Trick have found optimal solutions up to 14 x 14. For some larger sizes, the optimal solutions with some kind of symmetry are known: for instance, optimal rotationally symmetric and bilaterally symmetric solutions have been found for the 18 x 18 problem. As far as I am aware, larger optimal solutions are not currently known (January 2002).
This work is licensed under a Creative Commons Attribution 4.0 International License.