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 A253291 #6 Jul 23 2025 13:55:41 %S A253291 3844,23546,140536,1029888,7431136,52784020,376392916,2705942488, %T A253291 19441124904,139538118106,1001630063642,7192898044676,51663362450690, %U A253291 371000801080586,2664302414067690,19133126021242278,137412998986250836 %N A253291 Number of (n+1)X(3+1) 0..2 arrays with every 2X2 subblock sum differing from its neighbors horizontally, vertically, diagonally and antidiagonally. %C A253291 Column 3 of A253294 %H A253291 R. H. Hardin, <a href="/A253291/b253291.txt">Table of n, a(n) for n = 1..210</a> %e A253291 Some solutions for n=3 %e A253291 ..0..1..0..0....1..2..2..2....1..0..1..0....0..0..0..0....1..0..1..2 %e A253291 ..0..0..1..2....0..0..0..1....2..0..0..2....1..2..0..0....2..0..1..2 %e A253291 ..2..1..2..1....0..0..1..0....2..0..0..2....2..2..1..0....2..0..0..2 %e A253291 ..1..2..0..0....1..2..1..1....2..1..2..2....2..2..1..1....0..0..0..1 %K A253291 nonn %O A253291 1,1 %A A253291 _R. H. Hardin_, Dec 29 2014