There has been a lot of progress since my last update, catalogued on Achim Flammenkamp’s page. Most notably, Marijn Heule has come out of nowhere and smashed the size records using a new SAT solver; the record now stands at 76×76 (with four-fold rotational symmetry).

As for my GPU code, there hasn’t been any change there, just running it on larger systems for a longer time. One interesting result: the unique 47×47 solution with four-fold diagonal symmetry, displayed below. Thomas Prellberg has continued the search up to 57×57, but there hasn’t been another. Could this be the last in the symmetry class?