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cosh(arctanh(x)*cos(x))=1+1/2!*x^2-3/4!*x^4+45/6!*x^6+2457/8!*x^8...
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%I #6 Jul 07 2022 11:43:34

%S 1,1,-3,45,2457,161625,20549397,3457938757,772773915313,

%T 221864504883633,79479234590193325,34768359140993612893,

%U 18241340561609524790601,11306811847252896133698825

%N cosh(arctanh(x)*cos(x))=1+1/2!*x^2-3/4!*x^4+45/6!*x^6+2457/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Cosh[ArcTanh[x]Cos[x]],{x,0,nn}],x] Range[ 0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Jul 07 2022 *)

%K sign

%O 0,3

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