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A012725 exp(arctanh(x)*tan(x)) = 1+2/2!*x^2+28/4!*x^4+920/6!*x^6+54416/8!*x^8... 0
1, 2, 28, 920, 54416, 5056288, 678865856, 124425704832, 29873423298816, 9104340085891584, 3435702339713424384, 1573394503700675106816, 859935938676055185002496, 553085284375423405752918016 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..13.

FORMULA

a(n) ~ 2 * (2*n-1)! * (4*n)^(tan(1)/2) / GAMMA(tan(1)/2). - Vaclav Kotesovec, Oct 24 2013

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

Sequence in context: A090249 A264411 A009256 * A264637 A012756 A009403

Adjacent sequences:  A012722 A012723 A012724 * A012726 A012727 A012728

KEYWORD

nonn

AUTHOR

Patrick Demichel (patrick.demichel(AT)hp.com)

STATUS

approved

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Last modified November 15 01:22 EST 2019. Contains 329142 sequences. (Running on oeis4.)