A012675 sech(tanh(x)*tan(x))=1-12/4!*x^4+2128/8!*x^8+3482688/12!*x^12...

1, -12, 2128, 3482688, -28510476032, -29203453996032, 18429307563035250688, -709977989050867131727872, -146234048852276431866584563712, 20573909798214617779391304930951168

Offset

0,2

Links

Table of n, a(n) for n=0..9.

Mathematica

With[{nn=40}, Take[CoefficientList[Series[Sech[Tanh[x]Tan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -2, 4}]] (* Harvey P. Dale, Sep 10 2019 *)

Crossrefs

Sequence in context: A004823 A342964 A009063 * A175014 A101812 A064074

Adjacent sequences: A012672 A012673 A012674 * A012676 A012677 A012678

Keyword

sign

Author

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

Extensions

More terms from Harvey P. Dale, Sep 10 2019

Status

approved