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 A199566 #18 Aug 23 2024 16:28:28
%S A199566 4,32,284,2552,22964,206672,1860044,16740392,150663524,1355971712,
%T A199566 12203745404,109833708632,988503377684,8896530399152,80068773592364,
%U A199566 720618962331272,6485570660981444,58370135948832992,525331223539496924,4727981011855472312,42551829106699250804
%N A199566 a(n) = (7*9^n + 1)/2.
%H A199566 Vincenzo Librandi, <a href="/A199566/b199566.txt">Table of n, a(n) for n = 0..1000</a>
%H A199566 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (10,-9).
%F A199566 a(n) = 4*A187709(n).
%F A199566 a(n) = 9*a(n-1) - 4 for n > 0.
%F A199566 a(n) = 10*a(n-1) - 9*a(n-2) for n > 1.
%F A199566 G.f.: 4*(1-2*x)/((1-x)*(1-9*x)).
%F A199566 From _Elmo R. Oliveira_, Aug 23 2024: (Start)
%F A199566 E.g.f.: exp(x)*(7*exp(8*x) + 1)/2.
%F A199566 a(n) = A199567(n)/2. (End)
%t A199566 (7*9^Range[0,20]+1)/2 (* or *) LinearRecurrence[{10,-9},{4,32},20] (* _Harvey P. Dale_, Dec 08 2012 *)
%o A199566 (Magma) [(7*9^n+1)/2: n in [0..30]];
%Y A199566 Cf. A187709, A199567.
%K A199566 nonn,easy
%O A199566 0,1
%A A199566 _Vincenzo Librandi_, Nov 08 2011