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 A206872 #8 Mar 04 2018 16:14:57 %S A206872 7,49,211,1153,6139,31529,165783,867545,4529439,23698777,123917699, %T A206872 647878921,3387923179,17715041713,92629806615,484357042545, %U A206872 2532662234303,13243089222385,69247131747475,362087861614577,1893329530949883 %N A206872 Number of 3 X n 0..1 arrays avoiding 0 0 0 horizontally and 1 0 1 vertically. %C A206872 Row 3 of A206871. %H A206872 R. H. Hardin, <a href="/A206872/b206872.txt">Table of n, a(n) for n = 1..210</a> %F A206872 Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 27*a(n-3) - 13*a(n-4) + a(n-5) - 31*a(n-6) + 5*a(n-7) - 2*a(n-8) + 4*a(n-9). %F A206872 Empirical g.f.: x*(7 + 28*x + 15*x^2 - 12*x^3 - 29*x^4 - 26*x^5 + 3*x^6 + 2*x^7 + 4*x^8) / ((1 - x)*(1 - 2*x - 9*x^2 - 36*x^3 - 23*x^4 - 24*x^5 + 7*x^6 + 2*x^7 + 4*x^8)). - _Colin Barker_, Mar 04 2018 %e A206872 Some solutions for n=4: %e A206872 ..1..1..1..1....0..1..0..0....1..0..0..1....0..0..1..0....0..0..1..0 %e A206872 ..1..1..1..1....1..1..0..0....0..1..0..0....1..0..1..0....0..0..1..1 %e A206872 ..1..1..1..1....0..1..1..0....0..0..1..0....0..1..0..0....1..0..0..1 %Y A206872 Cf. A206871. %K A206872 nonn %O A206872 1,1 %A A206872 _R. H. Hardin_, Feb 13 2012