OFFSET
0,2
FORMULA
a(n) ~ (-1)^(n+1) * (2*n-1)! * ((exp(2)+1)/(exp(2)-1))^(2*n). - Vaclav Kotesovec, Feb 08 2015
MATHEMATICA
nn = 20; Table[(CoefficientList[Series[ArcTanh[ArcTan[x]^2], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Feb 08 2015 *)
CROSSREFS
KEYWORD
sign
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
a(0)=0 prepended by Vaclav Kotesovec, Feb 08 2015
STATUS
approved