A012501 - OEIS

%I #6 Sep 06 2020 14:23:08

%S 1,-1,21,-645,34153,-2966505,380114493,-67244074989,15717842398417,

%T -4694489063253585,1744673430747688805,-789702534539438543573,

%U 427739642844597474379833,-273184203052102765688128825

%N cos(cos(x)*arctan(x))=1-1/2!*x^2+21/4!*x^4-645/6!*x^6+34153/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Cos[Cos[x]ArcTan[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Sep 06 2020 *)

%K sign

%O 0,3

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