A012154 - OEIS

A012154

sech(tan(tan(x))) = 1-1/2!*x^2-11/4!*x^4-253/6!*x^6-9015/8!*x^8 ... .

1, -1, -11, -253, -9015, -362009, 2294909, 7143505067, 2709263596817, 958529947538255, 359564035447469189, 146418020203030157779, 64393370639942123229401, 29924760789755403918019639

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OFFSET

0,3

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Sech[Tan[Tan[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Sep 15 2023 *)

CROSSREFS

Sequence in context: A089298 A274129 A346896 * A377424 A009055 A009067

Adjacent sequences: A012151 A012152 A012153 * A012155 A012156 A012157

KEYWORD

sign

AUTHOR

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

STATUS

approved