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%I #13 Jun 29 2023 19:00:28
%S 8,35,143,575,2303,9215,36863,147455,589823,2359295,9437183,37748735,
%T 150994943,603979775,2415919103,9663676415,38654705663,154618822655,
%U 618475290623,2473901162495,9895604649983,39582418599935
%N a(n) = 9*4^n - 1.
%C Squares of the cotangents of the arcsins of 1/(3*2^n).
%H Vincenzo Librandi, <a href="/A114569/b114569.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 From _Philippe Deléham_, Nov 26 2008: (Start)
%F a(n) = 4*a(n-1) + 3, n>0; a(0)=8.
%F a(n) = 5*a(n-1) - 4*a(n-2), n>1; a(0)=8, a(1)=35.
%F G.f.: (8-5*x)/(1-5*x+4*x^2). (End)
%e a(2) = 143.
%t Table[(9*4^n) - 1, {n, 0, 23}] (* _Stefan Steinerberger_, Feb 16 2006 *)
%o (Magma) [9*4^n-1: n in [0..30]]; // _Vincenzo Librandi_, Oct 29 2011
%Y Cf. A024036, A097743, A156760.
%K easy,nonn
%O 0,1
%A Al Hakanson (hawkuu(AT)excite.com), Feb 16 2006
%E More terms from _Stefan Steinerberger_, Feb 16 2006
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