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%I #26 Sep 08 2022 08:44:38
%S 21,9261,4084101,1801088541,794280046581,350277500542221,
%T 154472377739119461,68122318582951682301,30041942495081691894741,
%U 13248496640331026125580781,5842587018385982521381124421
%N a(n) = 21^(2*n + 1).
%H Vincenzo Librandi, <a href="/A013726/b013726.txt">Table of n, a(n) for n = 0..200</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 (441).
%F From _Philippe Deléham_, Nov 28 2008: (Start)
%F a(n) = 441*a(n-1); a(0)=21.
%F G.f.: 21/(1-441*x). (End)
%F a(n) = A009965(A005408(n)). - _Wesley Ivan Hurt_, Feb 10 2014
%p seq(21^(2*n+1),n=0..10); # _Nathaniel Johnston_, Jun 25 2011
%t Table[21^(2 n + 1), {n, 0, 15}] (* _Wesley Ivan Hurt_, Feb 10 2014 *)
%o (Magma) [21^(2*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jun 26 2011
%o (PARI) a(n)=21^(2*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016
%Y Bisection of A009965 (21^n).
%Y Cf. A013708-A013725, A013727-A013729.
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_
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