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%I #20 May 25 2016 11:49:12
%S 1,1,2,-149,-14743,-1291124,-75141463,16904078101,12079897715342,
%T 5127055781374651,1591577436442791797,16734787827095948776,
%U -636181884940159502862223,-835452999214833112556297399,-749352506033895636346796223718,-390445159197257248842601279581749
%N E.g.f.: sqrt(-1+sqrt(1+3*cos(2*x)^2))/cos(2*x) [even terms only].
%C The odd power terms are zero because the e.g.f. is even.
%H Gheorghe Coserea, <a href="/A273047/b273047.txt">Table of n, a(n) for n = 0..200</a>
%e 1 + 1*x^2/2! + 2*x^4/4! - 149*x^6/6! - ...
%o (PARI)
%o x = 'x + O('x^31);
%o v = Vec(serlaplace(sqrt(-1+sqrt(1+3*cos(2*x)^2))/cos(2*x)));
%o vector((#v+1)\2, k, v[2*k-1])
%K sign
%O 0,3
%A _Gheorghe Coserea_, May 13 2016
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