Found by a dedicated fixed-cardinality search at modulus 901. Starting from witness #119, residue 236 was the least-conflicting possible 19th element (five ordered nontrivial solutions). A tabu search that evaluated every one-residue swap crossed the local barriers and found this set after 35,346 iterations. Direct enumeration gives exactly 19 solutions to a+3b=2c+2d, all diagonal.
David Renshaw · 2026-08-05 03:27:12 UTC