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 A229374 #9 Sep 14 2018 15:59:06 %S A229374 8,30,126,518,2138,8818,36374,150038,618890,2552850,10530214,43435926, %T A229374 179168218,739048370,3048489846,12574671318,51869078378,213954005138, %U A229374 882535756294,3640358873558,15016063240250,61939540321970 %N A229374 Number of n X 2 0..2 arrays avoiding 11 horizontally, 22 vertically and 00 diagonally or antidiagonally. %H A229374 R. H. Hardin, <a href="/A229374/b229374.txt">Table of n, a(n) for n = 1..210</a> %F A229374 Empirical: a(n) = 4*a(n-1) + a(n-2) - 2*a(n-3). %F A229374 Empirical g.f.: 2*x*(4 - x - x^2) / (1 - 4*x - x^2 + 2*x^3). - _Colin Barker_, Sep 14 2018 %e A229374 Some solutions for n=4: %e A229374 1 0 1 0 1 2 0 2 2 1 1 0 0 1 2 0 0 1 0 1 %e A229374 1 2 2 2 2 0 2 1 0 1 2 1 2 1 1 2 1 2 2 1 %e A229374 0 1 0 1 1 2 0 1 2 1 0 0 0 0 2 1 0 1 0 1 %e A229374 0 1 1 2 0 1 0 1 1 0 1 2 2 2 0 0 1 2 0 1 %Y A229374 Column 2 of A229380. %K A229374 nonn %O A229374 1,1 %A A229374 _R. H. Hardin_, Sep 21 2013