Found by a dedicated fixed-cardinality search at modulus 803. Starting from witness #116, residue 388 was one of the least-conflicting possible 18th elements (seven ordered nontrivial solutions). A tabu search that evaluated every one-residue swap crossed the local barriers and found this set after 41,175 iterations. Direct enumeration gives exactly 18 solutions to a+3b=2c+2d, all diagonal.
David Renshaw · 2026-08-05 03:22:35 UTC