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 A221173 #33 Dec 23 2023 08:43:31
%S A221173 -3,4,5,14,33,80,193,466,1125,2716,6557,15830,38217,92264,222745,
%T A221173 537754,1298253,3134260,7566773,18267806,44102385,106472576,257047537,
%U A221173 620567650,1498182837,3616933324,8732049485,21081032294,50894114073,122869260440,296632634953
%N A221173 a(0)=-3, a(1)=4; thereafter a(n) = 2*a(n-1) + a(n-2).
%H A221173 Reinhard Zumkeller, <a href="/A221173/b221173.txt">Table of n, a(n) for n = 0..1000</a>
%H A221173 José L. Ramírez, Gustavo N. Rubiano, and Rodrigo de Castro, <a href="http://arxiv.org/abs/1212.1368">A Generalization of the Fibonacci Word Fractal and the Fibonacci Snowflake</a>, arXiv preprint arXiv:1212.1368 [cs.DM], 2012-2014.
%H A221173 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,1).
%F A221173 a(n) = 10*A000129(n)-3*A000129(n+1). - _R. J. Mathar_, Jan 14 2013
%F A221173 G.f.: -(10*x-3) / (x^2+2*x-1). - _Colin Barker_, Jul 10 2015
%t A221173 LinearRecurrence[{2,1},{-3,4},50] (* _Harvey P. Dale_, Apr 09 2022 *)
%o A221173 (Haskell)
%o A221173 a221173 n = a221173_list !! n
%o A221173 a221173_list = -3 : 4 : zipWith (+)
%o A221173 (map (* 2) $ tail a221173_list) a221173_list
%o A221173 -- _Reinhard Zumkeller_, Jan 04 2013
%o A221173 (PARI) Vec(-(10*x-3)/(x^2+2*x-1) + O(x^100)) \\ _Colin Barker_, Jul 10 2015
%Y A221173 Cf. A000129, A078343, A221172, A221174, A221175.
%K A221173 sign,easy
%O A221173 0,1
%A A221173 _N. J. A. Sloane_, Jan 04 2013