OFFSET
0,2
COMMENTS
The two color classes are not interchangeable. Adjacent nodes cannot have the same color.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..500
FORMULA
Euler transform of A122086.
PROG
(PARI)
EulerT(v)={Vec(exp(x*Ser(dirmul(v, vector(#v, n, 1/n))))-1, -#v)}
TreeGf(N)={my(A=vector(N, j, 1)); for (n=1, N-1, A[n+1] = 1/n * sum(k=1, n, sumdiv(k, d, d*A[d]) * A[n-k+1] ) ); x*Ser(A)}
seq(n)={concat([1], EulerT(Vec(2*TreeGf(n) - TreeGf(n)^2)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Nov 02 2019
STATUS
approved