

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



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*n1])) \\ G. C. Greubel, Feb 12 2018


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



