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 A199684 #17 Oct 20 2022 07:57:15 %S A199684 5,41,401,4001,40001,400001,4000001,40000001,400000001,4000000001, %T A199684 40000000001,400000000001,4000000000001,40000000000001, %U A199684 400000000000001,4000000000000001,40000000000000001,400000000000000001,4000000000000000001 %N A199684 a(n) = 4*10^n+1. %H A199684 Vincenzo Librandi, <a href="/A199684/b199684.txt">Table of n, a(n) for n = 0..1000</a> %H A199684 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10). %F A199684 a(n) = 10*a(n-1)-9. %F A199684 a(n) = 11*a(n-1)-10*a(n-2). %F A199684 G.f.: (5-14*x)/((1-x)*(1-10*x)). %F A199684 E.g.f.: exp(x) + 4*exp(10*x). - _Stefano Spezia_, Oct 20 2022 %o A199684 (Magma) [4*10^n+1: n in [0..30]]; %Y A199684 Cf. A000533, A011557. %K A199684 nonn,easy %O A199684 0,1 %A A199684 _Vincenzo Librandi_, Nov 09 2011