OFFSET
1,3
COMMENTS
For precise definition, recurrence and asymptotics see the Pippenger reference.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
N. Pippenger, Enumeration of equicolorable trees, SIAM J. Discrete Math., 14 (2001), 93-115.
PROG
(PARI) \\ R is b.g.f of rooted trees x nodes, y in one part
R(n)={my(A=O(x)); for(j=1, 2*n, A = if(j%2, 1, y)*x*exp(sum(i=1, j, 1/i * subst(subst(A + x * O(x^(j\i)), x, x^i), y, y^i)))); A};
seq(n)={my(A=Pol(R(n))); my(r(x, y)=substvec(A, ['x, 'y], [x, y/x])); Vec(polcoeff((r(x, y/x) + r(y/x, x) - r(x, y/x)*r(y/x, x)), 0) + O(y*y^n))} \\ Andrew Howroyd, May 23 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Aug 04 2006
EXTENSIONS
Terms a(8) and beyond from Andrew Howroyd, May 21 2018
STATUS
approved