OFFSET
1,1
COMMENTS
Let C(n) denote the Catalan numbers A000108 and S(n) = Sum_{k>=1} a(k)/(2*k*(4*n+3)^(2*k)) then log(C(n)) = (1/2)*(n*log(16)-3*log(n+3/4)-log(Pi)+S(n)).
REFERENCES
Y. L. Luke, The Special Functions and their Approximations, Vol. 1. Academic Press, 1969.
LINKS
J. L. Fields, A note on the asymptotic expansion of a ratio of gamma functions, Proc. Edinburgh Math. Soc. 15 (1) (1966), 43-45.
D. Kessler and J. Schiff, The asymptotics of factorials, binomial coefficients and Catalan numbers. April 2006.
FORMULA
a(n) = -4^(2*n+1)*B_{2*n+1}(-1/4)/(2*n+1), B_{n}(x) the Bernoulli polynomials.
a(n) = 4 - E(2*n), E the Euler numbers A122045.
EXAMPLE
Let N = 4*n+3 then log(C(n)) = (n*log(16)-3*log(n+3/4)-log(Pi))/2+a(1)/(4*N^2)+a(2)/(8*N^4)+a(3)/(12*N^6)+a(4)/(16*N^8)+O(1/N^10).
MAPLE
A220422 := n -> 4 - euler(2*n):
PROG
CROSSREFS
KEYWORD
sign
AUTHOR
Peter Luschny, Dec 28 2012
STATUS
approved