OFFSET
0,2
FORMULA
a(n) ~ (2*n-1)! / r^(2*n), where r = 0.772419882704426062944736631601064953563... is the root of the equation arctanh(r)*tan(r) = 1. - Vaclav Kotesovec, Feb 05 2015
MATHEMATICA
With[{nn=30}, Flatten[{0, Take[CoefficientList[Series[ArcTanh[ArcTanh[x]Tan[x]], {x, 0, nn}], x] Range[0, nn]!, {3, -1, 2}]}]] (* Harvey P. Dale, Aug 26 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
Definition clarified by Harvey P. Dale, Aug 26 2014
Prepended missing a(0)=0 from Vaclav Kotesovec, Feb 05 2015
STATUS
approved