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A012839 sech(sec(x)*tanh(x))=1-1/2!*x^2+1/4!*x^4-97/6!*x^6+2945/8!*x^8... 0
1, -1, 1, -97, 2945, -148929, 15801729, -1624918817, 267458400513, -52723991194497, 12773658359030017, -3865567565691658721, 1370070916604727994497, -576252092267236760553793, 281775954919455982384816769, -158211465667174544221762575521 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..15.

MATHEMATICA

With[{nn=40}, Take[CoefficientList[Series[Sech[Sec[x]Tanh[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jun 20 2017 *)

CROSSREFS

Sequence in context: A241968 A020538 A075665 * A017813 A017760 A069419

Adjacent sequences:  A012836 A012837 A012838 * A012840 A012841 A012842

KEYWORD

sign

AUTHOR

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

EXTENSIONS

More terms from Harvey P. Dale, Jun 20 2017

STATUS

approved

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Last modified November 29 13:17 EST 2021. Contains 349416 sequences. (Running on oeis4.)