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cos(sec(x)*arcsinh(x))=1-1/2!*x^2-7/4!*x^4-145/6!*x^6-2063/8!*x^8...
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%I #6 Aug 04 2018 14:54:00

%S 1,-1,-7,-145,-2063,-128705,5154217,-510686033,254809389793,

%T -27371394484993,18728499608356185,-5038330344345849489,

%U 3197858289863468529361,-1630641802209014177997505

%N cos(sec(x)*arcsinh(x))=1-1/2!*x^2-7/4!*x^4-145/6!*x^6-2063/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Cos[Sec[x]ArcSinh[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Aug 04 2018 *)

%K sign

%O 0,3

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