OFFSET
1,4
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
FORMULA
For n > 1, a(n) = Sum_{k > 2} A206429(n, k).
E.g.f.: f(x) - x*(1 + f(x) + f(x)^2/2), where f(x) is the e.g.f. of A000169. - Andrew Howroyd, Jan 23 2020
EXAMPLE
Non-isomorphic representatives of the a(6) = 1026 trees (in the format root[branches]) are:
1[2,3,4[5[6]]]
1[2,3[4],5[6]]
1[2,3,4[5,6]]
1[2,3,4,5[6]]
1[2,3,4,5,6]
MATHEMATICA
lrt[set_]:=If[Length[set]==0, {}, Join@@Table[Apply[root, #]&/@Join@@Table[Tuples[lrt/@stn], {stn, sps[DeleteCases[set, root]]}], {root, set}]];
Table[Length[Select[lrt[Range[n]], Length[#]>2&]], {n, 6}]
PROG
(PARI) seq(n)={my(f=serreverse(x*exp(O(x^n) -x ))); Vec(serlaplace(f - x*(1 + f + f^2/2)), -n)} \\ Andrew Howroyd, Jan 23 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 21 2020
STATUS
approved