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 A253213 #17 Sep 22 2024 12:29:35
%S A253213 10,19,109,1009,10009,100009,1000009,10000009,100000009,1000000009,
%T A253213 10000000009,100000000009,1000000000009,10000000000009,
%U A253213 100000000000009,1000000000000009,10000000000000009,100000000000000009,1000000000000000009,10000000000000000009,100000000000000000009
%N A253213 a(n) = 10^n + 9.
%H A253213 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A253213 a(n) = 11*a(n-1) - 10*a(n-2) for n > 1.
%F A253213 G.f.: (10 - 91*x)/((1 - x)*(1 - 10*x)).
%F A253213 E.g.f.: exp(x)*(exp(9*x) + 9). - _Elmo R. Oliveira_, Sep 15 2024
%t A253213 Table[10^n + 9, {n, 0, 40}]
%t A253213 LinearRecurrence[{11,-10},{10,19},40] (* _Harvey P. Dale_, Jun 29 2018 *)
%o A253213 (Magma) [10^n+9: n in [0..30]];
%Y A253213 Cf. similar sequences listed in A253208.
%Y A253213 Cf. A170955.
%K A253213 nonn,easy
%O A253213 0,1
%A A253213 _Vincenzo Librandi_, Dec 30 2014
%E A253213 a(20) from _Elmo R. Oliveira_, Sep 15 2024
%E A253213 a(20) corrected by _Sean A. Irvine_, Sep 22 2024