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 A093357 #11 May 03 2024 14:16:00
%S A093357 0,4,20,88,368,1504,6080,24448,98048,392704,1571840,6289408,25161728,
%T A093357 100655104,402636800,1610579968,6442385408,25769672704,103078952960,
%U A093357 412316336128,1649266393088,6597067669504,26388274872320
%N A093357 Number of occurrences of pattern 2-1 after n iterations of morphism A007413.
%H A093357 S. Kitaev and T. Mansour, <a href="http://arXiv.org/abs/math.CO/0210170">Counting the occurrences of generalized patterns...</a>.
%H A093357 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6, -8).
%F A093357 a(1) = 0, a(n) = (3*4^(n-1) - 2^n)/2.
%F A093357 G.f.: 4*x*(1-x)/((1-2*x)*(1-4*x)).
%F A093357 a(1)=0, a(2)=4, a(3)=20, a(n)=6*a(n-1)-8*a(n-2). - _Harvey P. Dale_, Apr 04 2012
%F A093357 a(n) = 4*A010036(n-2). - _R. J. Mathar_, Apr 07 2022
%t A093357 Join[{0},Table[(3*4^(n-1)-2^n)/2,{n,2,30}]] (* or *) Join[{0}, LinearRecurrence[{6,-8},{4,20},30]] (* _Harvey P. Dale_, Apr 04 2012 *)
%o A093357 (PARI) a(n)=if(n==1,0,(3*4^(n-1)-2^n)/2)
%Y A093357 Cf. A007413, A010036.
%K A093357 nonn,easy
%O A093357 1,2
%A A093357 _Ralf Stephan_, Apr 27 2004