OFFSET
0,2
LINKS
Robert Israel, Table of n, a(n) for n = 0..225
FORMULA
a(n) ~ 2 * (2*n-1)! * (4*n)^(tan(1)/2) / GAMMA(tan(1)/2). - Vaclav Kotesovec, Oct 24 2013
EXAMPLE
1 + (2/2!)*x^2 + (28/4!)*x^4 + (920/6!)*x^6 + (54416/8!)*x^8 + ...
MAPLE
S:= series(exp(arctanh(x)*tan(x)), x, 31):
seq(coeff(S, x, j)*j!, j=0..30, 2); # Robert Israel, Aug 07 2023
MATHEMATICA
With[{nn=30}, Take[CoefficientList[Series[Exp[ArcTanh[x]Tan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Mar 25 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
STATUS
approved