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 A209231 #15 Jan 15 2013 17:18:32
%S A209231 0,0,0,0,1,3,6,10,15,22,33,51,80,125,193,295,449,684,1045,1600,2451,
%T A209231 3752,5738,8770,13403,20488,31326,47903,73251,112003,171244,261812,
%U A209231 400284,612008,935736,1430709,2187495,3344566,5113646,7818463,11953990
%N A209231 Number of binary words of length n such that there is at least one 0 and every run of consecutive 0's is of length >= 4.
%F A209231 O.g.f.: x^4/((1-x)*(1-2*x+x^2-x^5)), see Mathematica code for unsimplified form.
%e A209231 a(5) = 3 because we have: {0,0,0,0,0}, {0,0,0,0,1}, {1,0,0,0,0}.
%t A209231 nn=40; a=x^4/(1-x); CoefficientList[Series[(a+1)/((1-a x/(1-x)))*1/(1-x)-1/(1-x), {x,0,nn}], x]
%Y A209231 Cf. A000225, A077855, A130578.
%K A209231 nonn
%O A209231 0,6
%A A209231 _Geoffrey Critzer_, Jan 12 2013