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A012172 sec(tan(tanh(x)))=1+1/2!*x^2+5/4!*x^4+13/6!*x^6+41/8!*x^8... 0
1, 1, 5, 13, 41, 1529, -168851, 14151621, -1169749807, 65719458673, 5735813087573, -3489760303917315, 1000904582588332537, -229661980583327166359, 41111046331054702141117, -2494708337718975104154187, -2794803495926284988945714271 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Sec[Tan[Tanh[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Oct 15 2013 *)

CROSSREFS

Sequence in context: A085601 A147718 A111009 * A316536 A211383 A066873

Adjacent sequences:  A012169 A012170 A012171 * A012173 A012174 A012175

KEYWORD

sign

AUTHOR

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

EXTENSIONS

More terms from Harvey P. Dale, Oct 15 2013

STATUS

approved

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Last modified October 23 17:32 EDT 2019. Contains 328373 sequences. (Running on oeis4.)