OFFSET
0,2
FORMULA
a(n) ~ 4*(1-r^2) * (2*n)! / (((1-r^2)*Pi/tanh(r) + 2*sinh(r)) * r^(2*n+1)), where r = 0.907648090497239832680442727614114269985280667634413195506087... is the root of the equation arctanh(r)*sinh(r) = Pi/2. - Vaclav Kotesovec, Feb 06 2015
MATHEMATICA
nn = 20; Table[(CoefficientList[Series[Tan[ArcTanh[x]*Sinh[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Feb 06 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
a(0)=0 prepended by Vaclav Kotesovec, Feb 06 2015
STATUS
approved