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 A228756 #11 Sep 13 2018 06:08:03 %S A228756 8,21,168,780,4599,24246,134440,728537,3988862,21739002,118720559, %T A228756 647758554,3535719686,19295840383,105313615878,574764393110, %U A228756 3136909949941,17120293581344,93437607513222,509954720089427 %N A228756 Number of 4 X n binary arrays with top left element equal to 1 and no two ones adjacent horizontally or antidiagonally. %H A228756 R. H. Hardin, <a href="/A228756/b228756.txt">Table of n, a(n) for n = 1..210</a> %F A228756 Empirical: a(n) = a(n-1) + 20*a(n-2) + 27*a(n-3) - 14*a(n-4) - 25*a(n-5) + 4*a(n-6) + 5*a(n-7) - a(n-8). %F A228756 Empirical g.f.: x*(8 + 13*x - 13*x^2 - 24*x^3 + 4*x^4 + 5*x^5 - x^6) / ((1 + x)*(1 + 2*x - x^2)*(1 - 4*x - 9*x^2 + 5*x^3 + 4*x^4 - x^5)). - _Colin Barker_, Sep 13 2018 %e A228756 Some solutions for n=4: %e A228756 ..1..0..1..0....1..0..0..0....1..0..0..0....1..0..0..0....1..0..0..1 %e A228756 ..0..0..0..0....0..0..0..0....0..0..0..1....1..0..1..0....1..0..0..0 %e A228756 ..0..0..0..0....0..0..0..1....0..0..0..0....0..0..0..1....0..0..1..0 %e A228756 ..0..1..0..0....1..0..0..1....1..0..0..0....0..0..0..0....1..0..0..1 %Y A228756 Row 4 of A228754. %K A228756 nonn %O A228756 1,1 %A A228756 _R. H. Hardin_, Sep 02 2013