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 A203538 #7 Jun 02 2025 07:36:15 %S A203538 0,16,144,3364,30976,614656,8479744,129504400,1978826256,29961532836, %T A203538 454089995044,6895434839056,104626058201344,1587468792674704, %U A203538 24091008317030656,365573436678862864,5547427717263648804 %N A203538 Number of nX4 0..2 arrays with every element neighboring horizontally or vertically both a 0 and a 1. %C A203538 Column 4 of A203542 %H A203538 R. H. Hardin, <a href="/A203538/b203538.txt">Table of n, a(n) for n = 1..210</a> %e A203538 Some solutions for n=5 %e A203538 ..0..0..0..1....2..0..0..1....1..0..0..1....2..1..0..2....2..1..0..1 %e A203538 ..1..1..0..1....1..1..0..1....1..0..2..1....0..1..0..1....0..1..0..1 %e A203538 ..0..0..2..2....0..1..2..1....1..2..0..0....0..2..1..1....0..0..2..2 %e A203538 ..0..0..1..0....0..0..2..0....0..2..1..0....1..0..1..0....1..0..1..0 %e A203538 ..1..1..1..0....1..1..1..0....0..1..1..0....1..0..1..0....1..0..1..0 %K A203538 nonn %O A203538 1,2 %A A203538 _R. H. Hardin_ Jan 02 2012