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 A301946 #4 Mar 29 2018 12:42:28 %S A301946 1,5,20,83,342,1411,5820,24007,99026,408471,1684896,6950003,28667966, %T A301946 118252075,487776260,2012021183,8299356842,34233896031,141210898600, %U A301946 582478776747,2402658213526,9910689833651,40880459994636,168627213385143 %N A301946 Number of nX3 0..1 arrays with every element equal to 1, 2 or 3 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301946 Column 3 of A301951. %H A301946 R. H. Hardin, <a href="/A301946/b301946.txt">Table of n, a(n) for n = 1..210</a> %F A301946 Empirical: a(n) = 4*a(n-1) +a(n-2) -2*a(n-3) %e A301946 Some solutions for n=5 %e A301946 ..0..0..1. .0..0..1. .0..0..1. .0..0..0. .0..0..1. .0..0..0. .0..0..1 %e A301946 ..0..1..1. .0..1..1. .0..1..1. .0..1..1. .1..1..0. .0..0..1. .0..1..0 %e A301946 ..1..0..0. .0..0..1. .1..1..1. .0..0..0. .1..0..0. .0..1..1. .0..0..1 %e A301946 ..0..0..1. .0..1..1. .0..0..0. .1..1..1. .1..1..0. .1..1..0. .1..1..0 %e A301946 ..1..1..1. .1..1..1. .1..1..1. .1..0..0. .1..0..0. .0..0..0. .1..0..0 %Y A301946 Cf. A301951. %K A301946 nonn %O A301946 1,2 %A A301946 _R. H. Hardin_, Mar 29 2018