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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
OFFSET
0,2
LINKS
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
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Dec 16 2020
STATUS
approved