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 A301843 #4 Mar 27 2018 14:32:54 %S A301843 4,32,139,678,3182,15199,72514,346244,1653214,7893443,37688062, %T A301843 179946317,859175558,4102237937,19586633161,93518758201,446516665710, %U A301843 2131948036306,10179244758257,48602040050313,232056341426270,1107981178164225 %N A301843 Number of 3Xn 0..1 arrays with every element equal to 0, 1 or 2 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301843 Row 3 of A301841. %H A301843 R. H. Hardin, <a href="/A301843/b301843.txt">Table of n, a(n) for n = 1..210</a> %F A301843 Empirical: a(n) = 4*a(n-1) +3*a(n-2) +3*a(n-3) +2*a(n-4) -2*a(n-5) +2*a(n-6) -7*a(n-7) -3*a(n-8) +5*a(n-9) -4*a(n-10) -3*a(n-11) +a(n-12) for n>14 %e A301843 Some solutions for n=5 %e A301843 ..0..0..0..1..0. .0..1..0..1..1. .0..0..0..0..1. .0..1..0..0..1 %e A301843 ..1..0..1..1..1. .1..1..0..0..1. .1..1..0..1..0. .1..1..0..0..1 %e A301843 ..1..0..0..0..1. .0..1..1..0..1. .1..1..1..0..1. .0..1..0..0..0 %Y A301843 Cf. A301841. %K A301843 nonn %O A301843 1,1 %A A301843 _R. H. Hardin_, Mar 27 2018