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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
OFFSET
0,3
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
KEYWORD
sign
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
STATUS
approved