OFFSET
0,3
FORMULA
G.f.: 1/(1-x) = Sum_{n>=0} a(n) * x^n/(1+x)^[(n+1)*(n+2)/2 - 1].
a(n) = 1 - Sum_{j=0..n-1} a(j) * (-1)^(n-j) * C((j+1)(j+2)/2 + n-j-2, n-j) for n>0, with a(0)=1.
PROG
(PARI) {a(n)=if(n==0, 1, 1 - sum(j=0, n-1, a(j)*(-1)^(n-j)*binomial((j+1)*(j+2)/2-1+n-j-1, n-j)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 18 2008
STATUS
approved