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 A228755 #10 Sep 12 2018 15:08:53 %S A228755 4,8,39,126,482,1712,6277,22700,82580,299648,1088499,3952186,14352786, %T A228755 52119040,189266297,687294648,2495834292,9063317432,32912374319, %U A228755 119517358582,434013128786,1576067091632,5723300581661,20783486354532 %N A228755 Number of 3 X n binary arrays with top left element equal to 1 and no two ones adjacent horizontally or antidiagonally. %H A228755 R. H. Hardin, <a href="/A228755/b228755.txt">Table of n, a(n) for n = 1..210</a> %F A228755 Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - a(n-4). %F A228755 Empirical g.f.: x*(2 - x)*(2 + x) / (1 - 2*x - 6*x^2 + x^4). - _Colin Barker_, Sep 12 2018 %e A228755 Some solutions for n=4: %e A228755 ..1..0..0..0....1..0..1..0....1..0..0..1....1..0..0..0....1..0..1..0 %e A228755 ..1..0..1..0....0..0..0..0....0..0..0..0....0..0..0..1....0..0..0..1 %e A228755 ..0..0..0..0....0..1..0..1....0..1..0..1....0..1..0..0....1..0..0..1 %Y A228755 Row 3 of A228754. %K A228755 nonn %O A228755 1,1 %A A228755 _R. H. Hardin_, Sep 02 2013