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A012467 sech(arctan(x)^2) = 1 - 12/4!*x^4 + 480/6!*x^6 - 21168/8!*x^8 + ... 1
1, 0, -12, 480, -21168, 741120, 61942848, -29951061504, 8015861467392, -1745546459848704, 215844160641143808, 91751419512905687040, -109687232118939992862720, 71900040403600384794624000 (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[ArcTan[x]^2], {x, 0, nn}] , x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Apr 30 2012 *)

CROSSREFS

Sequence in context: A003749 A012395 A012687 * A009083 A012681 A009168

Adjacent sequences:  A012464 A012465 A012466 * A012468 A012469 A012470

KEYWORD

sign

AUTHOR

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

EXTENSIONS

Definition corrected by Harvey P. Dale, Apr 30 2012

STATUS

approved

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Last modified September 20 22:20 EDT 2019. Contains 327252 sequences. (Running on oeis4.)