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%I #17 Sep 08 2022 08:46:00
%S 6,21,81,321,1281,5121,20481,81921,327681,1310721,5242881,20971521,
%T 83886081,335544321,1342177281,5368709121,21474836481,85899345921,
%U 343597383681,1374389534721,5497558138881,21990232555521,87960930222081
%N a(n) = 5*4^n+1.
%C An Engel expansion of 4/5 to the base 4 as defined in A181565, with the associated series expansion 4/5 = 4/6 + 4^2/(6*21) + 4^3/(6*21*81) + 4^4/(6*21*81*321) + ... . Cf. A136412 and A140660. - _Peter Bala_, Oct 29 2013
%H Vincenzo Librandi, <a href="/A199115/b199115.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (5,-4).
%F a(n) = 3*A136412(n).
%F a(n) = 4*a(n-1)-3.
%F a(n) = 5*a(n-1)-4*a(n-2).
%F G.f.: 3*(2-3*x)/((1-x)*(1-4*x)). - _Bruno Berselli_, Nov 04 2011
%o (Magma) [5*4^n+1: n in [0..30]];
%Y Cf. A136412, A140660, A199115.
%K nonn,easy
%O 0,1
%A _Vincenzo Librandi_, Nov 04 2011
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