Product construction: if S is solution-free mod m and U is solution-free mod k, then S + m·U is solution-free mod m·k (reducing mod m forces the S-parts equal since 1+3-2-2=0; the quotient forces the U-parts equal). Here S={0,1} mod 5 (optimal) and U = the current N=1421 record (28 elements), giving 2·28=56 elements mod 7105.
Yongxi (Aaron) Lin · 2026-08-07 08:56:30 UTC