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A012395 sech(tan(x)*tan(x))=1-12/4!*x^4-480/6!*x^6-15792/8!*x^8... 1
1, 0, -12, -480, -15792, 387840, 232592448, 44951262720, 4538494871808, -1173690989322240, -1020600368000166912, -406075179314308669440, -50036577406600515366912, 87776293107173235762462720 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Sech[Tan[x]^2], {x, 0, nn}], x] Range[ 0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Feb 27 2013 *)

CROSSREFS

Sequence in context: A262584 A241226 A003749 * A012687 A012467 A009083

Adjacent sequences:  A012392 A012393 A012394 * A012396 A012397 A012398

KEYWORD

sign

AUTHOR

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

STATUS

approved

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Last modified September 20 01:58 EDT 2019. Contains 327207 sequences. (Running on oeis4.)