A009808 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A009808

Expansion of tanh(tan(tan(x))).

1, 2, 8, -400, -54016, -6545408, -886739968, -130488590336, -17561155108864, -157860190420992, 1926815267611213824, 1659729586864045162496, 1201487932870410723393536, 858251595734608746586832896

(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[Tanh[Tan[Tan[x]]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Jun 12 2016 *)

CROSSREFS

Sequence in context: A219994 A014185 A367998 * A035129 A284603 A329685

Adjacent sequences: A009805 A009806 A009807 * A009809 A009810 A009811

KEYWORD

sign

AUTHOR

R. H. Hardin

EXTENSIONS

Extended with signs by Olivier Gérard, Mar 15 1997

Prior Mathematica program replaced by Harvey P. Dale, Jun 12 2016

STATUS

approved