OFFSET
0,3
COMMENTS
Generally, for e.g.f. 1/(1-tan(p*x))^(1/p) is a(n) ~ n! * 2^(2*n+1/p) * p^n / (Gamma(1/p) * Pi^(n+1/p) * n^(1-1/p)).
FORMULA
a(n) ~ n! * 2^(3*n+1/2) / (Pi^(n+1) * sqrt(n)).
MATHEMATICA
CoefficientList[Series[1/(1 - Tan[2*x])^(1/2), {x, 0, 20}], x] * Range[0, 20]!
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vaclav Kotesovec, Jan 03 2014
STATUS
approved