OFFSET
0,3
FORMULA
a(n) ~ (2*n)! / r^(2*n+1), where r = 0.932706009172514... is the root of the equation cos(r)*log((1-r)/(1+r)) = -2. - Vaclav Kotesovec, Nov 02 2013
MATHEMATICA
Table[n!*SeriesCoefficient[ArcTanh[ArcTanh[x]*Cos[x]], {x, 0, n}], {n, 1, 41, 2}] (* Vaclav Kotesovec, Nov 02 2013 *)
With[{nn=40}, Take[CoefficientList[Series[ArcTanh[ArcTanh[x]Cos[x]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, May 20 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
STATUS
approved