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A012210 cosh(arctan(arctan(x)))=1+1/2!*x^2-15/4!*x^4+609/6!*x^6-48031/8!*x^8... 0
1, 1, -15, 609, -48031, 6247681, -1214813487, 330587407201, -120086685689663, 56186566871496961, -32929237073496552527, 23637878950680710828385, -20404361373477159717443295 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Cosh[ArcTan[ArcTan[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Ray Chandler, Nov 28 2016 *)

CROSSREFS

Sequence in context: A243227 A215899 A027505 * A203172 A081022 A049291

Adjacent sequences:  A012207 A012208 A012209 * A012211 A012212 A012213

KEYWORD

sign

AUTHOR

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

STATUS

approved

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Last modified October 20 05:51 EDT 2020. Contains 337897 sequences. (Running on oeis4.)