This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A253656 #7 Jul 23 2025 14:08:39 %S A253656 518,3318,25062,181308,1284808,9172142,65613880,467877898,3342085566, %T A253656 23863144636,170361773052,1216457665598,8685298245814,62011878783818, %U A253656 442766165059484,3161297854578070,22571505980125104,161159074186279688 %N A253656 Number of (n+1)X(2+1) 0..2 arrays with every 2X2 subblock diagonal maximum minus antidiagonal maximum unequal to its neighbors horizontally, vertically and nw-se diagonally. %C A253656 Column 2 of A253662 %H A253656 R. H. Hardin, <a href="/A253656/b253656.txt">Table of n, a(n) for n = 1..210</a> %H A253656 R. H. Hardin, <a href="/A253656/a253656.txt">Empirical recurrence of order 76</a> %F A253656 Empirical recurrence of order 76 (see link above) %e A253656 Some solutions for n=4 %e A253656 ..0..0..2....0..0..1....2..0..1....2..1..0....0..0..1....1..0..2....2..1..0 %e A253656 ..1..1..1....2..0..2....1..0..1....1..0..2....0..2..1....2..0..2....1..1..0 %e A253656 ..2..0..2....1..1..2....1..0..0....1..0..0....1..1..0....2..0..0....0..0..2 %e A253656 ..1..0..0....0..0..0....0..0..2....0..0..2....1..0..2....0..2..1....2..1..0 %e A253656 ..2..0..2....1..0..2....0..2..2....1..0..2....0..2..1....0..0..0....0..2..2 %K A253656 nonn %O A253656 1,1 %A A253656 _R. H. Hardin_, Jan 07 2015