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 A013806 #40 Apr 09 2022 02:26:34
%S A013806 17,1419857,118587876497,9904578032905937,827240261886336764177,
%T A013806 69091933913008732880827217,5770627412348402378939569991057,
%U A013806 481968572106750915091411825223071697,40254497110927943179349807054456171205137
%N A013806 a(n) = 17^(4*n+1).
%C A013806 As phi(a(n)) = (2*17^n)^4 is a perfect biquadrate (where phi is the Euler totient A000010), this is a subsequence of A078164 and A307690. - _Bernard Schott_, Mar 29 2022
%H A013806 Vincenzo Librandi, <a href="/A013806/b013806.txt">Table of n, a(n) for n = 0..100</a>
%H A013806 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.
%H A013806 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (83521).
%F A013806 a(0)=17, a(n)=83521*a(n-1). - _Harvey P. Dale_, May 21 2013
%F A013806 Sum_{n>=0} 1/a(n) = 4913/83520. - _Bernard Schott_, Mar 29 2022
%F A013806 Sum_{n>=0} (-1)^n/a(n) = 4913/83522. - _Bernard Schott_, Apr 08 2022
%t A013806 17^(4Range[0,10]+1) (* or *) NestList[83521#&,17,20] (* _Harvey P. Dale_, May 21 2013 *)
%o A013806 (Magma) [17^(4*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jul 06 2011
%Y A013806 Cf. A000010, A013776, A307690.
%Y A013806 Intersection of A001026 and A078164.
%K A013806 nonn,easy
%O A013806 0,1
%A A013806 _N. J. A. Sloane_