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 A202973 #8 Feb 19 2018 08:25:57 %S A202973 1,2,4,7,14,31,69,155,354,814,1875,4326,9993,23095,53387,123430, %T A202973 285394,659913,1525942,3528541,8159347,18867623,43629460,100888804, %U A202973 233295503,539473228,1247479743,2884676711,6670537293,15424975984,35668774074 %N A202973 Number of n X 2 0..1 arrays with every nonzero element less than or equal to at least two horizontal and vertical neighbors. %C A202973 Column 2 of A202979. %H A202973 R. H. Hardin, <a href="/A202973/b202973.txt">Table of n, a(n) for n = 1..210</a> %F A202973 Empirical: a(n) = 3*a(n-1) - 2*a(n-2) + 2*a(n-3) - 2*a(n-4) - a(n-5). %F A202973 Empirical g.f.: x*(1 - x - 3*x^3 - x^4) / (1 - 3*x + 2*x^2 - 2*x^3 + 2*x^4 + x^5). - _Colin Barker_, Feb 19 2018 %e A202973 Some solutions for n=5: %e A202973 ..0..0....0..0....1..1....0..0....1..1....0..0....1..1....1..1....1..1....1..1 %e A202973 ..0..0....1..1....1..1....1..1....1..1....0..0....1..1....1..1....1..1....1..1 %e A202973 ..0..0....1..1....0..0....1..1....0..0....0..0....1..1....1..1....1..0....0..1 %e A202973 ..1..1....0..0....1..1....1..1....0..0....0..0....0..0....1..1....1..1....1..1 %e A202973 ..1..1....0..0....1..1....0..0....0..0....0..0....0..0....1..1....1..1....1..1 %K A202973 nonn %O A202973 1,2 %A A202973 _R. H. Hardin_, Dec 26 2011