OFFSET
1,2
COMMENTS
See A145557 for the numerators, references and a W. Lang link.
FORMULA
a(n)=(1/2)*denominator(r(n)), with the rationals (in lowest terms) r(n):=sum(((-1)^(k+1))/(k*binomial(2*k,k)),k=1..n).
EXAMPLE
Rationals r(n) (in lowest terms): [1/2, 5/12, 13/30, 361/840, 31/72, 1193/2772, 31021/72072,...].
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
Wolfdieter Lang, Oct 17 2008
STATUS
approved