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 A301959 #4 Mar 29 2018 12:58:40 %S A301959 3,6,16,40,100,252,632,1588,3988,10016,25156,63180,158680,398532, %T A301959 1000932,2513888,6313748,15857276,39826296,100025620,251219060, %U A301959 630948512,1584656932,3979940588,9995808408,25104944036,63052250436,158358699360 %N A301959 Number of nX3 0..1 arrays with every element equal to 0, 1 or 4 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301959 Column 3 of A301964. %H A301959 R. H. Hardin, <a href="/A301959/b301959.txt">Table of n, a(n) for n = 1..210</a> %F A301959 Empirical: a(n) = a(n-1) +3*a(n-2) +2*a(n-3) %e A301959 Some solutions for n=5 %e A301959 ..0..1..0. .0..1..0. .0..0..1. .0..1..0. .0..1..0. .0..1..0. .0..0..1 %e A301959 ..1..0..1. .1..0..1. .1..0..1. .0..1..0. .0..1..0. .0..0..0. .1..0..1 %e A301959 ..1..1..1. .1..1..1. .1..1..1. .0..1..0. .0..1..1. .0..1..0. .0..1..0 %e A301959 ..1..0..0. .1..0..1. .1..0..0. .0..1..1. .0..0..1. .0..1..0. .0..1..0 %e A301959 ..1..1..0. .1..0..0. .1..1..0. .0..0..1. .1..0..1. .0..1..1. .0..1..0 %Y A301959 Cf. A301964. %K A301959 nonn %O A301959 1,1 %A A301959 _R. H. Hardin_, Mar 29 2018