OFFSET
0,2
COMMENTS
Equals the self-convolution of A093639.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..184
FORMULA
G.f. satisfies: A(x) = exp( 2*Sum_{n>=1} Sum_{k>=1} a(k)^n * (x^k)^n /n ) = Sum_{n>=0} a(n)*x^n. - Paul D. Hanna, Feb 13 2013
EXAMPLE
G.f.: A(x) = 1 + 2*x + 7*x^2 + 26*x^3 + 109*x^4 + 466*x^5 + 2142*x^6 +...
where
A(x) = 1/((1-x)*(1-2*x^2)*(1-7*x^3)*(1-26*x^4)*(1-109*x^4)*(1-466*x^4)*...)^2.
PROG
(PARI) a(n)=polcoeff(prod(i=0, n-1, 1/(1-a(i)*x^(i+1))^2)+x*O(x^n), n)
(PARI) a(n)=local(A=1+x); for(i=1, n, A=exp(2*sum(m=1, n, 1/m*sum(k=1, n, polcoeff(A+O(x^k), k-1)^m*x^(m*k)) +x*O(x^n)))); polcoeff(A, n)
for(n=0, 30, print1(a(n), ", ")) \\ Paul D. Hanna, Feb 13 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 07 2004
STATUS
approved