OFFSET
0,3
COMMENTS
Numerators of the q-Catalan numbers for q = 1/2. - John Keith, Feb 19 2021
FORMULA
G.f.: 1 = Sum_{n>=0} a(n)*x^n*prod_{k=0, n} (1-2^k*x) with a(0)=1.
a(n) = 2^(n*(n-1)/2)*b(n) where b(0)=1 and b(n)=sum(i=0,n-1,b(i)*b(n-1-i)/2^i). - Benoit Cloitre, Oct 25 2006
G.f.: Sum_{n>=0} a(n)*x^n/2^(n*(n+1)/2) = 1/(1 - (x/2)/(1 - (x/2^2)/(1 - (x/2^3)/(1 - (x/2^4)/(1 - (x/2^5)/(1 - ...)))))), a continued fraction. - Paul D. Hanna, Sep 28 2012
EXAMPLE
1 = (1-x) + 1*x*(1-x)*(1-2*x) + 3*x^2*(1-x)*(1-2*x)*(1-4*x) + 19*x^3*(1-x)*(1-2*x)*(1-4*x)*(1-8*x) + 243*x^4*(1-x)*(1-2*x)*(1-4*x)*(1-8*x)*(1-16*x) + ...
PROG
(PARI) {a(n)=if(n==0, 1, polcoeff(1-sum(k=0, n-1, a(k)*x^k*prod(j=0, k, 1-2^j*x+x*O(x^n))), n))}
{a(n)=local(CF=1+x*O(x^n)); for(k=1, n, CF=1/(1-x/2^(n-k+1)*CF)); 2^(n*(n+1)/2)*polcoeff(CF, n)} \\ Paul D. Hanna, Sep 28 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 10 2006
STATUS
approved