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 A202206 #22 Dec 23 2023 09:44:06
%S A202206 1,2,9,33,126,477,1809,6858,26001,98577,373734,1416933,5372001,
%T A202206 20366802,77216409,292749633,1109898126,4207943277,15953524209,
%U A202206 60484402458,229313780001,869394547377,3296124982134
%N A202206 a(n) = 3*a(n-1)+3*a(n-2) with a(0)=1 and a(1)=2.
%H A202206 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,3).
%F A202206 G.f.: (1-x)/(1-3*x-3*x^2).
%t A202206 LinearRecurrence[{3,3},{1,2},30] (* _Harvey P. Dale_, Aug 03 2020 *)
%o A202206 (PARI) Vec((1-x)/(1-3*x-3*x^2)+O(x^99)) \\ _Charles R Greathouse IV_, Jan 31 2012
%Y A202206 Cf. A104934, A112117.
%K A202206 nonn,easy
%O A202206 0,2
%A A202206 _Philippe Deléham_, Dec 14 2011