OFFSET
0,3
COMMENTS
The odd power terms are zero because the e.g.f. is even.
LINKS
Gheorghe Coserea, Table of n, a(n) for n = 0..200
EXAMPLE
1 + 1*x^2/2! + 2*x^4/4! - 149*x^6/6! - ...
PROG
(PARI)
x = 'x + O('x^31);
v = Vec(serlaplace(sqrt(-1+sqrt(1+3*cos(2*x)^2))/cos(2*x)));
vector((#v+1)\2, k, v[2*k-1])
CROSSREFS
KEYWORD
sign
AUTHOR
Gheorghe Coserea, May 13 2016
STATUS
approved