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 A015581 #40 Dec 30 2023 23:41:46
%S A015581 0,1,9,86,819,7801,74304,707741,6741189,64209406,611590599,5825362421,
%T A015581 55486214784,528502745161,5033955780369,47948115749126,
%U A015581 456702820643979,4350065964541441,41434107784092864,394657299879542981,3759086237836351149,35805062639924875246
%N A015581 a(n) = 9*a(n-1) + 5*a(n-2).
%C A015581 A linear 2nd-order recurrence.
%H A015581 Vincenzo Librandi, <a href="/A015581/b015581.txt">Table of n, a(n) for n = 0..1000</a>
%H A015581 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9,5).
%F A015581 G.f.: x/(1 - 9*x - 5*x^2). - _R. J. Mathar_, Dec 02 2007
%t A015581 Join[{a=0,b=1},Table[c=9*b+5*a;a=b;b=c,{n,60}]] (* _Vladimir Joseph Stephan Orlovsky_, Jan 27 2011 *)
%t A015581 LinearRecurrence[{9, 5}, {0, 1}, 30] (* _Vincenzo Librandi_, Nov 15 2012 *)
%o A015581 (Sage) [lucas_number1(n,9,-5) for n in range(0, 19)] # _Zerinvary Lajos_, Apr 26 2009
%o A015581 (Magma) [n le 2 select n-1 else 9*Self(n-1) + 5*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Nov 15 2012
%o A015581 (PARI) x='x+O('x^30); concat([0], Vec(x/(1-9*x-5*x^2))) \\ _G. C. Greubel_, Jan 06 2018
%Y A015581 Cf. A015579, A099371.
%K A015581 nonn,easy
%O A015581 0,3
%A A015581 _Olivier Gérard_
%E A015581 Extended by _T. D. Noe_, May 23 2011