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A012173 sech(tan(tanh(x)))=1-1/2!*x^2+5/4!*x^4-13/6!*x^6-1751/8!*x^8... 0
1, -1, 5, -13, -1751, 132871, -6935699, 5067579, 89435340497, -21076246089073, 3055142025663317, 13219661379785475, -235907327725301640967, 116095997487821991940759, -33017130566183943274793027, -532247345346868679322284213, 8810833241719412871344351850401 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..16.

MATHEMATICA

With[{nn=40}, Take[CoefficientList[Series[Sech[Tan[Tanh[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jan 15 2015 *)

CROSSREFS

Sequence in context: A012032 A121228 A201260 * A009143 A240765 A127317

Adjacent sequences:  A012170 A012171 A012172 * A012174 A012175 A012176

KEYWORD

sign

AUTHOR

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

EXTENSIONS

More terms from Harvey P. Dale, Jan 15 2015

STATUS

approved

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Last modified June 27 11:25 EDT 2017. Contains 288788 sequences.