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 A198700 #22 Aug 24 2024 10:52:46
%S A198700 10,109,1099,10999,109999,1099999,10999999,109999999,1099999999,
%T A198700 10999999999,109999999999,1099999999999,10999999999999,
%U A198700 109999999999999,1099999999999999,10999999999999999,109999999999999999,1099999999999999999,10999999999999999999,109999999999999999999
%N A198700 a(n) = 11*10^n - 1.
%H A198700 Vincenzo Librandi, <a href="/A198700/b198700.txt">Table of n, a(n) for n = 0..200</a>
%H A198700 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A198700 a(n) = 10*a(n-1) + 9.
%F A198700 a(n) = 11*a(n-1) - 10*a(n-2) for n > 1.
%F A198700 G.f.: (10-x)/((10*x-1)*(x-1)). - _R. J. Mathar_, Oct 29 2011
%F A198700 E.g.f.: exp(x)*(11*exp(9*x) - 1). - _Elmo R. Oliveira_, Aug 23 2024
%t A198700 (11 10^Range[0,20])-1 (* or *) LinearRecurrence[{11,-10},{10,109},20] (* _Harvey P. Dale_, Nov 29 2020 *)
%o A198700 (Magma) [11*10^n-1: n in [0..30]];
%Y A198700 Cf. A002283, A066007, A109002.
%Y A198700 Cf. A096209 (primes).
%K A198700 nonn,easy
%O A198700 0,1
%A A198700 _Vincenzo Librandi_, Oct 29 2011