A012211 sech(arctan(arctan(x)))=1-1/2!*x^2+21/4!*x^4-1149/6!*x^6+119305/8!*x^8...

1, -1, 21, -1149, 119305, -20082841, 4984310493, -1711500674389, 776816116717457, -450301381427975089, 324553968807761095973, -284661632752853556677805, 298518404617173649259722905

Offset

0,3

Links

Table of n, a(n) for n=0..12.

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sech[ArcTan[ArcTan[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Ray Chandler, Nov 28 2016 *)

Crossrefs

Sequence in context: A270505 A086098 A086875 * A297071 A036059 A036519

Adjacent sequences: A012208 A012209 A012210 * A012212 A012213 A012214

Keyword

sign

Author

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

Status

approved