OFFSET
0,3
FORMULA
G.f. satisfies: A(4*x) = Sum_{n>=0} 4^n*x^n/Product_{k=1..n} (1-4^n*x^k).
EXAMPLE
G.f.: A(x) = 1 + x + 2*x^2 + 6*x^3 + 35*x^4 + 394*x^5 + 8804*x^6 +...
where:
A(x) = 1 + x/(1-x) + x^2/((1-4*x)*(1-x^2)) + x^3/((1-16*x)*(1-4*x^2)*(1-x^3)) + x^4/((1-64*x)*(1-16*x^2)*(1-4*x^3)*(1-x^4)) +...
PROG
(PARI) {a(n)=local(A=1); polcoeff(sum(m=0, n, x^m/prod(k=1, m, 1-4^(m-k)*x^k +x*O(x^n))), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 17 2011
STATUS
approved