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

%I #24 Sep 08 2022 08:44:38

%S 3,81,2187,59049,1594323,43046721,1162261467,31381059609,847288609443,

%T 22876792454961,617673396283947,16677181699666569,450283905890997363,

%U 12157665459056928801,328256967394537077627,8862938119652501095929

%N a(n) = 3^(3*n + 1).

%H Vincenzo Librandi, <a href="/A013732/b013732.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 (27).

%F From _Philippe Deléham_, Nov 25 2008: (Start)

%F a(n) = 27*a(n-1); a(0)=3.

%F G.f.: 3/(1-27*x). (End)

%p seq(3^(3*n+1),n=0..15); # _Nathaniel Johnston_, Jun 26 2011

%t NestList[27#&,3,20] (* _Harvey P. Dale_, Apr 01 2018 *)

%o (Magma) [3^(3*n+1): n in [0..25]]; // _Vincenzo Librandi_, May 25 2011

%o (PARI) a(n)=3^(3*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016

%Y Cf. A013730, A013733, A013734.

%K nonn,easy

%O 0,1

%A _N. J. A. Sloane_