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 A190981 #27 Dec 23 2023 09:45:30
%S A190981 0,1,9,77,657,5605,47817,407933,3480129,29689429,253284345,2160801389,
%T A190981 18434075121,157263470533,1341634934313,11445660526685,97644405002913,
%U A190981 833017002919477,7106575406263641,60627110644694861,517217694177199185,4412450805016013221
%N A190981 a(n) = 9*a(n-1) - 4*a(n-2), with a(0)=0, a(1)=1.
%H A190981 Vincenzo Librandi, <a href="/A190981/b190981.txt">Table of n, a(n) for n = 0..500</a>
%H A190981 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9,-4).
%F A190981 G.f.: x/(1-9x+4*x^2). - _Philippe Deléham_, Oct 12 2011
%F A190981 E.g.f.: (2/sqrt(65))*exp(9*x/2)*sinh(sqrt(65)*x/2). - _G. C. Greubel_, Aug 25 2022
%t A190981 LinearRecurrence[{9,-4}, {0,1}, 50]
%o A190981 (Magma) [2^(n-1)*Evaluate(ChebyshevU(n), 9/4): n in [0..30]]; // _G. C. Greubel_, Aug 25 2022
%o A190981 (SageMath)
%o A190981 A190981 = BinaryRecurrenceSequence(9,-4,0,1)
%o A190981 [A190981(n) for n in (0..30)] # _G. C. Greubel_, Aug 25 2022
%Y A190981 Cf. A190958 (index to generalized Fibonacci sequences).
%K A190981 nonn,easy
%O A190981 0,3
%A A190981 _Vladimir Joseph Stephan Orlovsky_, May 24 2011