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 A199691 #16 Jun 12 2025 00:47:20
%S A199691 12,111,1101,11001,110001,1100001,11000001,110000001,1100000001,
%T A199691 11000000001,110000000001,1100000000001,11000000000001,
%U A199691 110000000000001,1100000000000001,11000000000000001,110000000000000001,1100000000000000001,11000000000000000001,110000000000000000001
%N A199691 a(n) = 11*10^n + 1.
%H A199691 Vincenzo Librandi, <a href="/A199691/b199691.txt">Table of n, a(n) for n = 0..1000</a>
%H A199691 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A199691 a(n) = 10*a(n-1) - 9.
%F A199691 a(n) = 11*a(n-1) - 10*a(n-2).
%F A199691 G.f.: 3*(4-7*x)/((1-x)*(1-10*x)).
%F A199691 From _Elmo R. Oliveira_, Jun 10 2025: (Start)
%F A199691 E.g.f.: exp(x)*(1 + 11*exp(9*x)).
%F A199691 a(n) = 3*A199690(n). (End)
%t A199691 11 10^Range[0,20]+1 (* or *) LinearRecurrence[{11,-10},{12,111},20] (* _Harvey P. Dale_, Jan 29 2023 *)
%o A199691 (Magma) [11*10^n+1: n in [0..30]];
%Y A199691 Cf. A199690.
%K A199691 nonn,easy
%O A199691 0,1
%A A199691 _Vincenzo Librandi_, Nov 09 2011