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 A199215 #22 May 07 2025 14:57:05
%S A199215 5,21,101,501,2501,12501,62501,312501,1562501,7812501,39062501,
%T A199215 195312501,976562501,4882812501,24414062501,122070312501,610351562501,
%U A199215 3051757812501,15258789062501,76293945312501,381469726562501,1907348632812501,9536743164062501,47683715820312501
%N A199215 a(n) = 4*5^n + 1.
%H A199215 Vincenzo Librandi, <a href="/A199215/b199215.txt">Table of n, a(n) for n = 0..1000</a>
%H A199215 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-5).
%F A199215 a(n) = 5*a(n-1) - 4.
%F A199215 a(n) = 6*a(n-1) - 5*a(n-2).
%F A199215 G.f.: (5-9*x)/((1-x)*(1-5*x)). - _Bruno Berselli_, Nov 04 2011
%F A199215 E.g.f.: exp(x)*(1 + 4*exp(4*x)). - _Elmo R. Oliveira_, May 07 2025
%t A199215 4*5^Range[0,30]+1 (* or *) LinearRecurrence[{6,-5},{5,21},30] (* _Harvey P. Dale_, Mar 30 2018 *)
%o A199215 (Magma) [4*5^n+1: n in [0..30]];
%K A199215 nonn,easy
%O A199215 0,1
%A A199215 _Vincenzo Librandi_, Nov 04 2011