OFFSET
0,3
COMMENTS
Compare to a g.f. of Fibonacci numbers (A000045):
Sum_{n>=0} x^n * Product_{k=1..n} (k + x)/(1 + k*x).
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..230
FORMULA
a(n) ~ sqrt(Pi) * n^(2*n+1/2) / (sqrt(1-log(2)) * exp(2*n) * (log(2))^(2*n+1)). - Vaclav Kotesovec, Oct 28 2014
EXAMPLE
G.f.: A(x) = 1 + x + 8*x^2 + 120*x^3 + 3516*x^4 + 166328*x^5 +...
where
A(x) = 1 + x*(1+x)/(1+x) + x^2*(2+x)*(4+x)/((1+2*x)*(1+4*x)) + x^3*(3+x)*(6+x)*(9+x)/((1+3*x)*(1+6*x)*(1+9*x)) + x^4*(4+x)*(8+x)*(12+x)*(16+x)/((1+4*x)*(1+8*x)*(1+12*x)*(1+16*x)) +...
PROG
(PARI) {a(n)=polcoeff(sum(m=0, n, x^m*prod(k=1, m, m*k+x+x*O(x^n))/prod(k=1, m, 1+m*k*x+x*O(x^n))), n)}
for(n=0, 20, print1(a(n), ", ") )
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 02 2013
STATUS
approved