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%I #19 Sep 08 2022 08:45:52
%S 21,42,84,168,336,672,1344,2688,5376,10752,21504,43008,86016,172032,
%T 344064,688128,1376256,2752512,5505024,11010048,22020096,44040192,
%U 88080384,176160768,352321536,704643072,1409286144,2818572288,5637144576,11274289152,22548578304,45097156608
%N a(n) = 21*2^n.
%H Vincenzo Librandi, <a href="/A175805/b175805.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (2).
%F G.f.: 21/(1-2*x).
%F a(n) = 2*a(n-1). - _Vincenzo Librandi_, Jul 08 2016
%t Table[21 2^n, {n, 0, 40}] (* _Vincenzo Librandi_, Jul 08 2016 *)
%o (Magma)[21*2^n: n in [0..100]]
%o (PARI) a(n)=21<<n \\ _Charles R Greathouse IV_, Oct 07 2015
%Y Cf. A159256.
%K nonn,easy
%O 0,1
%A _Vincenzo Librandi_, Dec 05 2010
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