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a(n) = 3^(4n).
1

%I #14 Jan 25 2020 01:41:55

%S 81,6561,531441,43046721,3486784401,282429536481,22876792454961,

%T 1853020188851841,150094635296999121,12157665459056928801,

%U 984770902183611232881,79766443076872509863361,6461081889226673298932241,523347633027360537213511521

%N a(n) = 3^(4n).

%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 (81).

%F a(n) = 81^n.

%F G.f.: 81*x/(1-81*x). - _Philippe Deléham_, Nov 25 2008

%t 3^(4*Range[20]) (* or *) NestList[81#&,81,20] (* _Harvey P. Dale_, Apr 09 2012 *)

%Y Cf. A000244, A001019, A009971.

%K nonn

%O 1,1

%A Douglas Winston (douglas.winston(AT)srupc.com), Jan 05 2004

%E More terms from _Harvey P. Dale_, Apr 09 2012