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 A181239 #6 Mar 26 2018 14:25:25 %S A181239 16,178,2066,23858,275690,3185462,36806846,425288998,4914052362, %T A181239 56780001474,656071271338,7580653428086,87591560417790, %U A181239 1012087088416198,11694280472399626,135122952690874754,1561294205914890890 %N A181239 Number of n X 4 binary matrices with no 2 X 2 circuit having pattern 0101 in any orientation. %C A181239 Column 4 of A181245. %H A181239 R. H. Hardin, <a href="/A181239/b181239.txt">Table of n, a(n) for n=1..200</a> %F A181239 Empirical: a(n) = 10*a(n-1) + 20*a(n-2) - 21*a(n-3) - 30*a(n-4) + 8*a(n-5). %F A181239 Empirical g.f.: 2*x*(8 + 9*x - 17*x^2 - 13*x^3 + 4*x^4) / (1 - 10*x - 20*x^2 + 21*x^3 + 30*x^4 - 8*x^5). - _Colin Barker_, Mar 26 2018 %Y A181239 Cf. A181245. %K A181239 nonn %O A181239 1,1 %A A181239 _R. H. Hardin_, Oct 10 2010