A012230 sech(arctan(tanh(x)))=1-1/2!*x^2+21/4!*x^4-1101/6!*x^6+109001/8!*x^8...

1, -1, 21, -1101, 109001, -17491001, 4139085981, -1355308485701, 586612833746961, -324261948714025201, 222851423174495787941, -186365710421614910029501, 186332939048243649892744921

Offset

0,3

Links

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

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sech[ArcTan[Tanh[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Oct 01 2017 *)

Crossrefs

Sequence in context: A143003 A193156 A012183 * A357314 A270505 A086098

Adjacent sequences: A012227 A012228 A012229 * A012231 A012232 A012233

Keyword

sign

Author

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

Status

approved