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A012221 sech(arctan(arcsinh(x)))=1-1/2!*x^2+17/4!*x^4-769/6!*x^6+66401/8!*x^8... 1
1, -1, 17, -769, 66401, -9313281, 1927198833, -551835917697, 208856369686977, -100945109069282817, 60655475821737151953, -44346899335054478649345, 38762487400695339770533665 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..12.

CROSSREFS

Sequence in context: A283579 A294757 A176233 * A012144 A265190 A308490

Adjacent sequences:  A012218 A012219 A012220 * A012222 A012223 A012224

KEYWORD

sign

AUTHOR

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

STATUS

approved

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Last modified October 23 16:40 EDT 2020. Contains 337969 sequences. (Running on oeis4.)