A009817 Expansion of e.g.f. tanh(tan(x)*x) (even powers only).

0, 2, 8, -144, -11264, -323840, 36347904, 8388294656, 620426657792, -168731721990144, -79627879039631360, -11099857853570613248, 5627175549005859913728, 4469405304978356270268416

Offset

0,2

Links

Iain Fox, Table of n, a(n) for n = 0..231 (first 101 terms from Vincenzo Librandi)

Maple

S:= series(tanh(tan(x)*x), x, 41):
seq(coeff(S, x, n)*n!, n=0..40, 2); # Robert Israel, Dec 21 2017

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Tanh[Tan[x]*x], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Oct 28 2013 *)

Prog

(PARI) first(n) = x='x+O('x^(2*n-1)); vecextract(Vec(serlaplace(tanh(tan(x)*x)), -2*n), (4^n - 1)/3) \\ Iain Fox, Dec 21 2017

Crossrefs

Cf. A000182, A003718, A009707, A024257.

Sequence in context: A304798 A154908 A166356 * A124105 A079613 A091299

Adjacent sequences: A009814 A009815 A009816 * A009818 A009819 A009820

Keyword

sign

Author

R. H. Hardin, Mar 15 1996

Extensions

Extended with signs by Olivier Gérard, Mar 15 1997

Prior Mathematica program replaced by Harvey P. Dale, Oct 28 2013

Status

approved