OFFSET
0,3
COMMENTS
Radius of convergence of e.g.f. is |x| < r where r = 0.6516970063076... satisfies cosh(r) = cos(r)/r.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
FORMULA
a(n) ~ n!/((sin(r)+cosh(r)+sinh(r)*r)*r^(n+1)), where r = 0.6516970063... is the root of the equation r*cosh(r) = cos(r). - Vaclav Kotesovec, Jun 27 2013
EXAMPLE
E.g.f.: A(x) = 1 + x + 3*x^2/2! + 15*x^3/3! + 89*x^4/4! + 685*x^5/5! +...
MATHEMATICA
CoefficientList[Series[1/(Cos[x]-x*Cosh[x]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jun 27 2013 *)
PROG
(PARI) {a(n)=n!*polcoeff(1/(cos(x+x*O(x^n))-x*cosh(x+x*O(x^n))), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jan 29 2012
STATUS
approved