OFFSET
0,2
FORMULA
G.f.: 1 = Sum_{k>=0} a(k)*x^k*(1-x)^(2 + k*(k-1)/2).
EXAMPLE
1 = 1*(1-x)^2 + 2*x*(1-x)^2 + 3*x^2*(1-x)^3 +
7*x^3*(1-x)^5 + 26*x^4*(1-x)^8 + 141*x^5*(1-x)^12 +...
PROG
(PARI) {a(n)=polcoeff(1-sum(k=0, n-1, a(k)*x^k*(1-x+x*O(x^n))^(2+k*(k-1)/2)), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jun 04 2005
STATUS
approved