A012454 - OEIS

%I #6 Jan 12 2016 10:58:59

%S 1,0,12,0,17360,-241920,186158016,-11413642240,7726026430720,

%T -1212323504480256,892608906281741312,-274005660019568705536,

%U 234514059257417538031616,-119571044071522301122641920

%N sec(arctan(x)*tan(x))=1+12/4!*x^4+17360/8!*x^8-241920/10!*x^10...

%t With[{nn=30},Take[CoefficientList[Series[Sec[ArcTan[x]Tan[x]],{x,0,nn}], x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Jan 12 2016 *)

%K sign

%O 0,3

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