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A339782 Number of homeomorphically irreducible leaf colored trees with n leaves of 2 colors. 5
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 (list; graph; refs; listen; history; text; internal format)
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: A301877 A221172 A116054 * A176621 A099527 A345276

Adjacent sequences:  A339779 A339780 A339781 * A339783 A339784 A339785

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Dec 16 2020

STATUS

approved

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Last modified May 24 12:01 EDT 2022. Contains 354033 sequences. (Running on oeis4.)