OFFSET
0,2
FORMULA
a(n) ~ 2^(3/2) * (2*n)! / (sqrt(Pi) * sinh(sqrt(2*Pi)) * (tanh(sqrt(Pi/2)))^(2*n)). - Vaclav Kotesovec, Feb 06 2015
MATHEMATICA
With[{nn=30}, Take[CoefficientList[Series[Tan[ArcTanh[x]^2], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Mar 31 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
Definition clarified by Harvey P. Dale, Mar 31 2013
STATUS
approved