OFFSET
0,3
EXAMPLE
A(x) = 1 + x*(1+x)^2 + x^2*(1+x)^2*(1+2x)^2 + x^3*(1+x)^2*(1+2x)^2*(1+3x)^2 +...
PROG
(PARI) a(n)=polcoeff(sum(k=0, n, x^k*prod(j=0, k, 1+j*x+x*O(x^n))^2), n)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Oct 28 2006
STATUS
approved