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 A203357 #8 Jun 04 2018 05:47:39 %S A203357 3,20,102,565,3042,16538,89610,486103,2635899,14295131,77522409, %T A203357 420410296,2279906481,12364072580,67051079697,363621959233, %U A203357 1971943176024,10693963589630,57993991716273,314504819239756,1705578083028348 %N A203357 Number of n X 3 binary arrays with every 1 immediately preceded by 0 to the left or above. %C A203357 Column 3 of A203362. %H A203357 R. H. Hardin, <a href="/A203357/b203357.txt">Table of n, a(n) for n = 1..210</a> %F A203357 Empirical: a(n) = 3*a(n-1) +12*a(n-2) +6*a(n-3) +a(n-4). %F A203357 Empirical g.f.: x*(3 + 11*x + 6*x^2 + x^3) / (1 - 3*x - 12*x^2 - 6*x^3 - x^4). - _Colin Barker_, Jun 04 2018 %e A203357 Some solutions for n=5: %e A203357 ..0..1..0....0..1..0....0..0..0....0..0..0....0..0..1....0..0..1....0..1..0 %e A203357 ..0..0..0....0..0..0....0..0..1....0..1..1....1..0..1....1..0..0....0..1..0 %e A203357 ..0..0..1....0..0..1....1..1..0....0..1..0....0..0..0....0..1..0....0..0..1 %e A203357 ..0..0..0....0..0..1....0..1..0....1..0..1....1..0..0....0..1..0....0..1..0 %e A203357 ..0..1..0....0..1..0....0..1..0....0..0..0....0..0..0....0..1..0....0..1..1 %Y A203357 Cf. A203362. %K A203357 nonn %O A203357 1,1 %A A203357 _R. H. Hardin_, Dec 31 2011