A012805 - OEIS

%I #6 Nov 28 2016 20:47:34

%S 1,-1,33,-1377,99649,-11796673,2017677153,-471591223841,

%T 144742585812609,-56447611418620289,27268126498786597537,

%U -15985843319019939868385,11182140682997302960743361

%N arctan(sec(x)*arctan(x))=x-1/3!*x^3+33/5!*x^5-1377/7!*x^7+99649/9!*x^9...

%t With[{nn=30},Take[CoefficientList[Series[ArcTan[Sec[x]*ArcTan[x]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Ray Chandler_, Nov 28 2016 *)

%K sign

%O 0,3

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