A012621 sech(arcsinh(x)*tan(x))=1-12/4!*x^4-120/6!*x^6+1680/8!*x^8...

1, 0, -12, -120, 1680, 367680, 12095424, -560956032, -447394871040, -8068784621568, -1294533276204032, 6639186363172284416, -1043706052752056152064, 641443809049086939217920

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sech[ArcSinh[x]Tan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Aug 27 2019 *)

Crossrefs

Sequence in context: A239188 A200163 A012565 * A102341 A174561 A009078

Adjacent sequences: A012618 A012619 A012620 * A012622 A012623 A012624

Keyword

sign

Author

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

Status

approved