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A009750 Expansion of e.g.f. tan(x)*tan(tan(x)), even powers only. 2
0, 2, 24, 688, 36992, 3234304, 418499584, 75077748736, 17816420974592, 5399699170000896, 2034070241589854208, 932012713402719797248, 510363278595553899839488, 329128604050609873851777024, 246881504912875480553409740800, 213119748914997017969817425018880 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..224

FORMULA

a(n) ~ (2*n)! * 4 * Pi / ((4+Pi^2) * arctan(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 24 2015

MATHEMATICA

nn = 20; Table[(CoefficientList[Series[Tan[x]*Tan[Tan[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 24 2015 *)

PROG

(PARI) x='x+O('x^50); v=Vec(serlaplace(tan(x)*tan(tan(x)))); concat([0], vector(#v\2, n, v[2*n-1])) \\ G. C. Greubel, Feb 12 2018

CROSSREFS

Sequence in context: A012375 A012750 A174997 * A030438 A012723 A069150

Adjacent sequences:  A009747 A009748 A009749 * A009751 A009752 A009753

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested by Olivier Gérard, Mar 15 1997

STATUS

approved

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Last modified February 24 21:12 EST 2020. Contains 332210 sequences. (Running on oeis4.)