OFFSET
0,2
EXAMPLE
The a(1) = 3 cases correspond to a single edge which can be attached to zero, one or both of the roots.
PROG
(PARI) \\ See A339063 for G.
seq(n)={my(A=O(x*x^n)); Vec((G(2*n, x+A, [1, 1]) + G(2*n, x+A, [2]))/2)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Nov 22 2020
STATUS
approved