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A012818 arctanh(sec(x)*sinh(x))=x+6/3!*x^3+140/5!*x^5+8456/7!*x^7... 0
1, 6, 140, 8456, 957840, 174293856, 46514037440, 17115342333056, 8304761365213440, 5137820023434733056, 3947233200665413667840, 3686931444647916864505856, 4114664615209642258282352640 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..12.

FORMULA

a(n) ~ (2*n)! / r^(2*n+1), where r = 0.7032906588639654058999212003816567397131... is the root of the equation sec(r)*sinh(r) = 1. - Vaclav Kotesovec, Feb 05 2015

MATHEMATICA

nn = 20; Table[(CoefficientList[Series[ArcTanh[Sec[x]*Sinh[x]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 05 2015 *)

CROSSREFS

Sequence in context: A193185 A322625 A012785 * A078450 A193502 A059488

Adjacent sequences:  A012815 A012816 A012817 * A012819 A012820 A012821

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified October 4 19:10 EDT 2022. Contains 357239 sequences. (Running on oeis4.)