OFFSET
1,2
COMMENTS
For precise definition, recurrence and asymptotics see the Pippenger reference.
An equicolorable tree is a tree which can be colored with two colors with adjacent nodes having different colors and there being an equal number of nodes of each color. - Andrew Howroyd, May 21 2018
REFERENCES
N. Pippenger, Enumeration of equicolorable trees, SIAM J. Discrete Math., 14 (2001), 93-115.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
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), 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