OFFSET
0,3
COMMENTS
Compare to g.f. G(x) of A000081 (number of rooted trees with n nodes), which satisfies: G(x) = exp( Sum_{n>=1} x^n*G(x^n)/n ).
EXAMPLE
G.f.: A(x) = 1 + x + 2*x^2 + 5*x^3 + 15*x^4 + 50*x^5 + 191*x^6 +...
The g.f. satisfies:
log(A(x)) = x*A(x+x^2) + x^2*A(x^2+x^4)/2 + x^3*A(x^3+x^6)/3 +...
PROG
(PARI) {a(n)=local(A=1+x); for(i=1, n, A=exp(sum(m=1, n, x^m*subst(A, x, x^m+x^(2*m)+x*O(x^n))/m))); polcoeff(A, n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 06 2011
STATUS
approved