OFFSET
0,3
FORMULA
a(n) = (1/2)*((-1)^n+A000364(n)). Also cosh(log(cos(x))) = 1/2*(cos(x)+1/cos(x)) is the reciprocal of the e.g.f. of A012009. - Peter Bala, Dec 02 2011
MATHEMATICA
terms = 15; s = Cosh[Log[Cos[x]]] + O[x]^(2*terms); CoefficientList[s, x^2] * Table[(2n)!, {n, 0, terms-1}] (* Jean-François Alcover, May 22 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
Confirmed by N. J. A. Sloane, Dec 17 2011
STATUS
approved