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%I #6 Nov 28 2019 15:06:59
%S 1,1,1,49,-447,78561,-5655231,1014069393,-187639949439,51144433721793,
%T -16631972691697791,6837287119716744945,-3357388632038371909695,
%U 1969419543279480607781025
%N sec(arcsin(arctan(x)))=1+1/2!*x^2+1/4!*x^4+49/6!*x^6-447/8!*x^8...
%t With[{nn=30},Take[CoefficientList[Series[Sec[ArcSin[ArcTan[x]]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Nov 28 2019 *)
%K sign
%O 0,4
%A Patrick Demichel (patrick.demichel(AT)hp.com)