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 A190980 #28 Dec 23 2023 09:43:09
%S A190980 0,1,9,78,675,5841,50544,437373,3784725,32750406,283399479,2452344093,
%T A190980 21220898400,183631053321,1589016784689,13750257902238,
%U A190980 118985270766075,1029616663187961,8909594156393424,77097497417976933,667148694292612125,5773045756379578326
%N A190980 a(n) = 9*a(n-1) - 3*a(n-2), with a(0)=0, a(1)=1.
%H A190980 Vincenzo Librandi, <a href="/A190980/b190980.txt">Table of n, a(n) for n = 0..500</a>
%H A190980 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9,-3).
%F A190980 G.f.: x/(1-9*x+3*x^2). - _Philippe Deléham_, Oct 12 2011
%t A190980 LinearRecurrence[{9,-3}, {0,1}, 50]
%t A190980 CoefficientList[Series[x/(1-9*x+3*x^2), {x,0,50}], x] (* _G. C. Greubel_, Jan 14 2018 *)
%o A190980 (PARI) x='x+O('x^30); concat([0], Vec(x/(1-9*x+3*x^2))) \\ _G. C. Greubel_, Jan 14 2018
%o A190980 (Magma) I:=[0,1]; [n le 2 select I[n] else 9*Self(n-1) - 3*Self(n-2): n in [1..30]]; // _G. C. Greubel_, Jan 14 2018
%Y A190980 Cf. A190958 (index to generalized Fibonacci sequences).
%K A190980 nonn
%O A190980 0,3
%A A190980 _Vladimir Joseph Stephan Orlovsky_, May 24 2011