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 A301902 #6 Sep 21 2018 21:48:05 %S A301902 1,2,3,7,16,43,117,330,935,2667,7616,21775,62273,178130,509563, %T A301902 1457727,4170224,11930147,34129757,97638522,279324735,799093699, %U A301902 2286051744,6539949991,18709526921,53524323778,153122698291,438054310967 %N A301902 Number of n X 3 0..1 arrays with every element equal to 0, 2 or 3 horizontally or antidiagonally adjacent elements, with upper left element zero. %H A301902 R. H. Hardin, <a href="/A301902/b301902.txt">Table of n, a(n) for n = 1..210</a> %F A301902 Empirical: a(n) = 3*a(n-1) +a(n-2) -4*a(n-3). %e A301902 Some solutions for n=5 %e A301902 ..0..1..1. .0..1..0. .0..1..1. .0..1..1. .0..1..1. .0..1..1. .0..1..0 %e A301902 ..1..1..0. .0..1..1. .1..1..0. .1..1..1. .1..1..0. .1..1..1. .0..1..0 %e A301902 ..1..1..1. .1..1..1. .1..1..0. .0..1..1. .0..1..0. .0..1..1. .0..1..0 %e A301902 ..0..1..1. .0..1..1. .1..1..1. .0..1..1. .0..1..1. .1..1..0. .0..1..0 %e A301902 ..1..1..0. .1..1..0. .1..1..0. .1..1..0. .1..1..0. .0..1..0. .0..1..0 %Y A301902 Column 3 of A301906. %K A301902 nonn %O A301902 1,2 %A A301902 _R. H. Hardin_, Mar 28 2018