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A009723 Expansion of tan(tanh(x)/cos(x)). 0
1, 3, 57, 1995, 128881, 12775059, 1796958633, 342118793307, 84276974508769, 26141579246291235, 9956883572644073241, 4570240365824839488747, 2487549038143714062879313, 1584207614996350912703688627 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..13.

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Tan[Tanh[x]/Cos[x]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Dec 15 2014 *)

CROSSREFS

Sequence in context: A053725 A053774 A254570 * A069992 A012196 A012090

Adjacent sequences:  A009720 A009721 A009722 * A009724 A009725 A009726

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested Mar 15 1997 by Olivier Gérard.

Prior Mathematica program replaced by Harvey P. Dale, Dec 15 2014

STATUS

approved

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Last modified February 22 21:26 EST 2018. Contains 299469 sequences. (Running on oeis4.)