OFFSET
2,2
PROG
(PARI) a(n)=if(n<2, 0, (matrix(n, n, m, j, binomial(m-1, j-1)*binomial(m, j-1)/j)^-1)[n, 2])
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Feb 02 2005
STATUS
approved