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 A199685 #21 Sep 16 2024 03:11:05
%S A199685 6,51,501,5001,50001,500001,5000001,50000001,500000001,5000000001,
%T A199685 50000000001,500000000001,5000000000001,50000000000001,
%U A199685 500000000000001,5000000000000001,50000000000000001,500000000000000001,5000000000000000001,50000000000000000001,500000000000000000001
%N A199685 a(n) = 5*10^n + 1.
%H A199685 Vincenzo Librandi, <a href="/A199685/b199685.txt">Table of n, a(n) for n = 0..1000</a>
%H A199685 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A199685 a(n) = 3*A126109(n).
%F A199685 a(n) = 10*a(n-1) - 9.
%F A199685 a(n) = 11*a(n-1) - 10*a(n-2).
%F A199685 G.f.: 3*(2-5*x)/((1-x)*(1-10*x)).
%F A199685 E.g.f.: exp(x)*(5*exp(9*x) + 1). - _Elmo R. Oliveira_, Sep 15 2024
%t A199685 LinearRecurrence[{11,-10},{6,51},30] (* _Harvey P. Dale_, Apr 06 2013 *)
%o A199685 (Magma) [5*10^n+1: n in [0..30]];
%o A199685 (PARI) a(n)=5*10^n+1 \\ _Charles R Greathouse IV_, Oct 16 2015
%Y A199685 Cf. A126109.
%K A199685 nonn,easy
%O A199685 0,1
%A A199685 _Vincenzo Librandi_, Nov 09 2011