OFFSET
2,2
FORMULA
E.g.f.: (1/sqrt(1-x^2))*((x/(1-x))^2)/2!.
a(n) = (n!/2!)*Sum_{k=0..floor((n-2)/2)} binomial(2*k, k)*(n-2*k-1)/(4^k), n >= 2.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Aug 23 2005
STATUS
approved