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 A199687 #17 Jun 10 2025 16:33:02
%S A199687 8,71,701,7001,70001,700001,7000001,70000001,700000001,7000000001,
%T A199687 70000000001,700000000001,7000000000001,70000000000001,
%U A199687 700000000000001,7000000000000001,70000000000000001,700000000000000001,7000000000000000001,70000000000000000001,700000000000000000001
%N A199687 a(n) = 7*10^n + 1.
%H A199687 Vincenzo Librandi, <a href="/A199687/b199687.txt">Table of n, a(n) for n = 0..1000</a>
%H A199687 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A199687 a(n) = 10*a(n-1) - 9.
%F A199687 a(n) = 11*a(n-1) - 10*a(n-2).
%F A199687 G.f.: (8-17*x)/((1-x)*(1-10*x)).
%F A199687 E.g.f.: exp(x)*(1 + 7*exp(9*x)). - _Elmo R. Oliveira_, Jun 10 2025
%t A199687 7*10^Range[0,20]+1 (* or *) LinearRecurrence[{11,-10},{8,71},20] (* _Harvey P. Dale_, May 29 2018 *)
%o A199687 (Magma) [7*10^n+1: n in [0..30]];
%K A199687 nonn,easy
%O A199687 0,1
%A A199687 _Vincenzo Librandi_, Nov 09 2011