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A012239 sech(arctan(arctanh(x)))=1-1/2!*x^2+5/4!*x^4-109/6!*x^6+2729/8!*x^8... 0
1, -1, 5, -109, 2729, -196281, 9832173, -1827291621, 102520239057, -58512018759921, -121510420621227, -5298654687807230685, -895543588646311726215, -1180050438628226991259305 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Sech[ArcTan[ArcTanh[x]]], {x, 0, nn}], x]Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Mar 03 2013 *)

CROSSREFS

Sequence in context: A142510 A195552 A318292 * A012121 A014180 A012122

Adjacent sequences:  A012236 A012237 A012238 * A012240 A012241 A012242

KEYWORD

sign

AUTHOR

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

STATUS

approved

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Last modified September 20 20:12 EDT 2019. Contains 327247 sequences. (Running on oeis4.)