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 A135423 #28 Sep 08 2022 08:45:32
%S A135423 3,23,203,1823,16403,147623,1328603,11957423,107616803,968551223,
%T A135423 8716961003,78452649023,706073841203,6354664570823,57191981137403,
%U A135423 514727830236623,4632550472129603,41692954249166423,375236588242497803
%N A135423 a(n) = (5*9^n + 1)/2.
%H A135423 Vincenzo Librandi, <a href="/A135423/b135423.txt">Table of n, a(n) for n = 0..1000</a>
%H A135423 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10,-9).
%F A135423 a(n) = 9*a(n-1) - 4 for n>0, a(0)=3.
%F A135423 O.g.f.: (1/(1-x) - 5/(9*x-1))/2. - _R. J. Mathar_, Feb 19 2008
%F A135423 a(n) = 10*a(n-1) - 9*a(n-2). - _Vincenzo Librandi_, Nov 08 2011
%F A135423 E.g.f.: (1/2)*( 5*exp(9*x) + exp(x) ). - _G. C. Greubel_, Oct 14 2016
%t A135423 Table[ (5*9^n + 1)/2, {n,0,25}] (* or *) LinearRecurrence[{10, -9}, {3, 23}, 25] (* _G. C. Greubel_, Oct 14 2016 *)
%o A135423 (Magma) [(5*9^n+1)/2: n in [0..30]]; // _Vincenzo Librandi_, Nov 08 2011
%Y A135423 Bisection of A057198. Cf. A191450.
%K A135423 nonn,easy
%O A135423 0,1
%A A135423 _Paul Curtz_, Feb 18 2008
%E A135423 More terms from _R. J. Mathar_, Feb 19 2008
%E A135423 Definition rewritten (with Mathar's formula) from _Bruno Berselli_, Nov 08 2011