A012180 - OEIS

%I #6 Sep 06 2023 19:45:33

%S 1,2,16,48,-29696,-6049792,-1262426112,-308569372672,-89297625350144,

%T -30123113337716736,-11520007513318621184,-4775431672418431664128,

%U -1952929261585732032528384,-545214673336986589066166272

%N tanh(tan(arctanh(x)))=x+2/3!*x^3+16/5!*x^5+48/7!*x^7-29696/9!*x^9...

%t With[{nn=30},Take[CoefficientList[Series[Tanh[Tan[ArcTanh[x]]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Sep 06 2023 *)

%K sign

%O 0,2

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