Found by a randomized fixed-cardinality local search at N=1103. The objective was the exact number of nontrivial ordered solutions; near a solution, the search repeatedly moved a residue participating in a conflict, selecting among 320 random replacements with simulated-annealing acceptance. Search seed 701 found this set after 134,988 moves. Independently checked by literal enumeration of all 20^4 ordered quadruples: exactly 20 solutions, all diagonal.
David Renshaw · 2026-08-05 03:58:22 UTC