A009698 - OEIS

A009698

Expansion of tan(tan(x))*sin(x).

0, 2, 12, 358, 19352, 1709194, 222722596, 40122780142, 9543330683696, 2895895566420498, 1091590070839432764, 500335689476146083190, 274027979513688992336584, 176734166480671985581245594

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OFFSET

0,2

LINKS

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

FORMULA

a(n) ~ (2*n)! * 8 * Pi / ((4+Pi^2)^(3/2) * arctan(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 23 2015

MATHEMATICA

Tan[ Tan[ x ] ]*Sin[ x ] (* Even Part *)

nn = 20; Table[(CoefficientList[Series[Sin[x]*Tan[Tan[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 23 2015 *)

CROSSREFS

Sequence in context: A192892 A105231 A009398 * A012724 A012624 A335829

Adjacent sequences: A009695 A009696 A009697 * A009699 A009700 A009701

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested Mar 15 1997 by Olivier Gérard.

STATUS

approved