A339782 Number of homeomorphically irreducible leaf colored trees with n leaves of 2 colors.

1, 2, 3, 4, 11, 30, 105, 380, 1555, 6650, 30091, 140592, 677396, 3336280, 16752485, 85444832, 441757114, 2310561412, 12208670550, 65088056150, 349773085560, 1893030193232, 10311145350621, 56489805467868, 311113902447810, 1721697849252838, 9569947189448379, 53410284955104654

Offset

0,2

Links

Andrew Howroyd, Table of n, a(n) for n = 0..500

Example

There are two trees for a(4):
          o         o    o
          |         |    |
      o---o---o     o----o
          |         |    |
          o         o    o
The first of these can have the 4 leaves colored in 5 indistinguishable ways and the second can have the 4 leaves colored in 6 indistinguishable ways so a(4) = 5 + 6 = 11.

Prog

(PARI) U(25, 2) \\ See A339779 for U(n, k).

Crossrefs

Column k=2 of A339779.

Sequence in context: A369438 A221172 A116054 * A176621 A370365 A099527

Adjacent sequences: A339779 A339780 A339781 * A339783 A339784 A339785

Keyword

nonn

Author

Andrew Howroyd, Dec 16 2020

Status

approved