OFFSET
0,3
COMMENTS
Compare to a g.f. of the Pell numbers (A000129):
Sum_{n>=0} x^n * Product_{k=1..n} (2*k + x)/(1 + 2*k*x) = 1/(1-2*x-x^2).
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..280
FORMULA
a(n) = Sum_{k=0..n} A231171(n,k)*(-2)^k for n>=0.
a(n) ~ 2^(n+1) * n! / (3 * (log(3))^(n+1)). - Vaclav Kotesovec, Nov 02 2014
EXAMPLE
G.f.: A(x) = 1 + x + 2*x^2 + 12*x^3 + 98*x^4 + 956*x^5 + 10936*x^6 +...
where
A(x) = 1 + x*(1-2*x)/(1-2*x) + x^2*(1-2*x)*(2-2*x)/((1-2*x)*(1-4*x)) + x^3*(1-2*x)*(2-2*x)*(3-2*x)/((1-2*x)*(1-4*x)*(1-6*x)) + x^4*(1-2*x)*(2-2*x)*(3-2*x)*(4-2*x)/((1-2*x)*(1-4*x)*(1-6*x)*(1-8*x)) +...
PROG
(PARI) {a(n)=polcoeff(sum(m=0, n, x^m*prod(k=1, m, (k-2*x)/(1-2*k*x +x*O(x^n)))), n)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 05 2013
STATUS
approved