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A012798 arctanh(sec(x)*tan(x))=x+7/3!*x^3+185/5!*x^5+12367/7!*x^7... 0
1, 7, 185, 12367, 1558865, 316097527, 94003171145, 38543705698687, 20840298552277025, 14366953364916735847, 12299504390976449116505, 12801737583190675819689007, 15920156445351352463114729585 (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)! / (arctan(sqrt((sqrt(5)-1)/2)))^(2*n+1). - Vaclav Kotesovec, Feb 05 2015

MATHEMATICA

nn = 20; Table[(CoefficientList[Series[ArcTanh[Sec[x]*Tan[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: A152436 A176338 A012843 * A297765 A193811 A296234

Adjacent sequences:  A012795 A012796 A012797 * A012799 A012800 A012801

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified September 24 15:33 EDT 2021. Contains 347643 sequences. (Running on oeis4.)