OFFSET
0,4
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..250
FORMULA
E.g.f.: cosh(log(1+tan(x))).
a(n) ~ n! * (-1)^n * 4^n / Pi^(n+1). - Vaclav Kotesovec, Jan 22 2015
MATHEMATICA
CoefficientList[Series[(1 + (1 + Tan[x])^2)/(2*(1 + Tan[x])), {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 22 2015 *)
PROG
(PARI) x='x+O('x^30); Vec(serlaplace(cosh(log(1+tan(x))))) \\ G. C. Greubel, Jul 28 2018
(Magma) m:=30; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!(Cosh(Log(1+Tan(x))))); [Factorial(n-1)*b[n]: n in [1..m]]; // G. C. Greubel, Jul 28 2018
CROSSREFS
KEYWORD
sign,easy
AUTHOR
EXTENSIONS
Extended with signs by Olivier Gérard, Mar 15 1997
STATUS
approved