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a(n) = 17^(4*n+1).
2

%I #40 Apr 09 2022 02:26:34

%S 17,1419857,118587876497,9904578032905937,827240261886336764177,

%T 69091933913008732880827217,5770627412348402378939569991057,

%U 481968572106750915091411825223071697,40254497110927943179349807054456171205137

%N a(n) = 17^(4*n+1).

%C 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 Vincenzo Librandi, <a href="/A013806/b013806.txt">Table of n, a(n) for n = 0..100</a>

%H Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.

%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (83521).

%F a(0)=17, a(n)=83521*a(n-1). - _Harvey P. Dale_, May 21 2013

%F Sum_{n>=0} 1/a(n) = 4913/83520. - _Bernard Schott_, Mar 29 2022

%F Sum_{n>=0} (-1)^n/a(n) = 4913/83522. - _Bernard Schott_, Apr 08 2022

%t 17^(4Range[0,10]+1) (* or *) NestList[83521#&,17,20] (* _Harvey P. Dale_, May 21 2013 *)

%o (Magma) [17^(4*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jul 06 2011

%Y Cf. A000010, A013776, A307690.

%Y Intersection of A001026 and A078164.

%K nonn,easy

%O 0,1

%A _N. J. A. Sloane_