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 A206450 #13 Jun 30 2021 12:31:59
%S A206450 4,16,64,255,1016,4048,16128,64257,256012,1020000,4063872,16191231,
%T A206450 64508912,257015648,1023998720,4079803649,16254705684,64761807088,
%U A206450 258023229632,1028013114879,4095797753832,16318429208240,65015693603328
%N A206450 Number of 0..3 arrays of length n avoiding the consecutive pattern 0..3.
%C A206450 Column 3 of A206455.
%H A206450 R. H. Hardin, <a href="/A206450/b206450.txt">Table of n, a(n) for n = 1..210</a>
%H A206450 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,0,-1).
%F A206450 a(n) = 4*a(n-1) -a(n-4).
%F A206450 Empirical: a(n) = sum{i in 0..floor(n/4)} ((-1)^i*4^(n-4*i)*binomial(n-3*i,i)).
%F A206450 g.f.: x*(4 - x^3) / (1 - 4*x + x^4). - _Colin Barker_, Feb 23 2018
%Y A206450 Cf. A206455.
%K A206450 nonn,easy
%O A206450 1,1
%A A206450 _R. H. Hardin_, Feb 07 2012