OFFSET
0,2
FORMULA
a(n) = -9^n*binomial(n/3,n)/(2n/3 - 1).
PROG
(PARI) a(n)=9^n*binomial(n/3, n)/(1-2*n/3)
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Dec 02 2007
STATUS
approved