OFFSET
0,3
FORMULA
G.f. : g/(1-f) where f/(1-f)^3=x and g=1-f; a(n)=(-1)^n*sum{k=0..floor(n/2), ((3k+1)/(2n-k+1))*binomial(3n-3k, n-2k)}.
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Jul 06 2005
STATUS
approved