OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
V. P. Johnson, Enumeration Results on Leaf Labeled Trees, Ph. D. Dissertation, Univ. Southern Calif., 2012.
MAPLE
a:= proc(n) option remember; `if`(n<2, 3*n, `if`(n::odd, 0,
(t-> t*(1-t)/2)(a(n/2)))+add(a(i)*a(n-i), i=1..n/2))
end:
seq(a(n), n=1..25); # Alois P. Heinz, Sep 23 2018
MATHEMATICA
a[n_] := a[n] = If[n < 2, 3 n, If[OddQ[n], 0, (# (1 - #)/2 &)[a[n/2]]] + Sum[a[i] a[n - i], {i, 1, n/2}]];
Array[a, 25] (* Jean-François Alcover, Sep 02 2019, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 22 2012
EXTENSIONS
a(7) corrected and terms a(11) and beyond from Andrew Howroyd, Sep 22 2018
STATUS
approved