A012687 sech(tanh(x)*arctan(x))=1-12/4!*x^4+480/6!*x^6-18480/8!*x^8...

1, 0, -12, 480, -18480, 176640, 149396544, -38742692352, 6743113079040, -363222941859840, -455485254371044352, 322516524038804660224, -135316725169663246512128, 19655917963465137568481280

Offset

0,3

Links

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

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sech[Tanh[x]ArcTan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Apr 19 2019 *)

Crossrefs

Sequence in context: A241226 A003749 A012395 * A012467 A009083 A012681

Adjacent sequences: A012684 A012685 A012686 * A012688 A012689 A012690

Keyword

sign

Author

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

Status

approved