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A009106
Expansion of e.g.f. cos(x)/cos(tan(x)), even powers only.
1
1, 0, 8, 216, 12032, 1075328, 140944000, 25464568832, 6065774456832, 1842040163078144, 694620312112857088, 318448731218429771776, 174429761567957718302720, 112504917152076237383401472
OFFSET
0,3
LINKS
FORMULA
a(n) ~ (2*n)! * 16 / ((4+Pi^2)^(3/2) * arctan(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 22 2015
MATHEMATICA
nn = 20; Table[(CoefficientList[Series[Cos[x]*Sec[Tan[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 22 2015 *)
PROG
(PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x)/cos(tan(x)))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jul 26 2018
CROSSREFS
Sequence in context: A009072 A002897 A024289 * A000442 A268471 A342598
KEYWORD
nonn
AUTHOR
EXTENSIONS
Extended and signs tested by Olivier Gérard, Mar 15 1997
STATUS
approved