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 A198969 #16 Sep 08 2022 08:46:00
%S A198969 5,49,445,4009,36085,324769,2922925,26306329,236756965,2130812689,
%T A198969 19177314205,172595827849,1553362450645,13980262055809,
%U A198969 125822358502285,1132401226520569,10191611038685125,91724499348166129,825520494133495165
%N A198969 (11*9^n-1)/2.
%H A198969 Vincenzo Librandi, <a href="/A198969/b198969.txt">Table of n, a(n) for n = 0..1000</a>
%H A198969 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (10,-9).
%F A198969 a(n) = 9*a(n-1)+4. a(n) = 10*a(n-1)-9*a(n-2), n>1.
%F A198969 G.f.: (5 - x)/(1 - 10*x + 9*x^2). - _Vincenzo Librandi_, Jan 03 2013
%t A198969 CoefficientList[Series[(5 - x)/(1 - 10*x + 9*x^2), {x, 0, 30}], x] (* _Vincenzo Librandi_, Jan 03 2013 *)
%t A198969 LinearRecurrence[{10,-9},{5,49},20] (* _Harvey P. Dale_, Oct 16 2021 *)
%o A198969 (Magma) [(11*9^n-1)/2: n in [0..20]]
%K A198969 nonn,easy
%O A198969 0,1
%A A198969 _Vincenzo Librandi_, Nov 01 2011