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 A286974 #6 Apr 05 2020 23:28:43 %S A286974 0,5,50,538,3932,32253,238532,1875212,14222474,110768815,851356180, %T A286974 6619388000,51243150110,398853561051,3101596551513,24188042117410, %U A286974 188685917890136,1474444397004861,11529364760294089,90260751863587788 %N A286974 Number of n X 3 0..1 arrays with the number of 1's horizontally or vertically adjacent to some 0 two less than the number of 0's adjacent to some 1. %C A286974 Column 3 of A286979. %H A286974 R. H. Hardin, <a href="/A286974/b286974.txt">Table of n, a(n) for n = 1..210</a> %e A286974 Some solutions for n=4 %e A286974 ..1..0..1. .0..0..1. .0..1..0. .0..1..1. .1..0..0. .1..1..0. .0..1..1 %e A286974 ..0..0..1. .1..1..0. .0..1..1. .0..0..0. .0..0..0. .1..1..0. .0..0..1 %e A286974 ..1..0..0. .0..0..1. .0..1..0. .1..1..0. .1..0..1. .1..0..0. .0..0..1 %e A286974 ..0..1..0. .0..1..0. .0..1..0. .0..1..0. .1..0..0. .0..0..1. .1..0..0 %Y A286974 Cf. A286979. %K A286974 nonn %O A286974 1,2 %A A286974 _R. H. Hardin_, May 17 2017