OFFSET
0,4
FORMULA
a(n) = (2*n)! * [x^(2*n)] sin(x*tan(x/2)).
EXAMPLE
sin(x*tan(x/2)) = x^2/2! + x^4/4! - 12*x^6/6! - 193*x^8/8! - 2365*x^10/10! - 18552*x^12/12! + ...
MATHEMATICA
nmax = 17; Table[(CoefficientList[Series[Sin[x Tan[x/2]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Dec 21 2017
STATUS
approved