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A220829

Number of unrooted binary leaf-multi-labeled trees with n leaves on the label set [2], with each label used at least once.

0, 1, 2, 4, 10, 27, 74, 226, 710, 2354, 8010, 28189, 101094, 370119, 1375198, 5181003, 19740940, 75990173, 295100800, 1155106357, 4553312866, 18063117153, 72069297826, 289053128879, 1164870009786, 4714970819402, 19161572076550, 78162885020942, 319940035684684, 1313799822309748

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..500

V. P. Johnson, Enumeration Results on Leaf Labeled Trees, Ph. D. Dissertation, Univ. Southern Calif., 2012.

FORMULA

a(n) = A220826(n) - 2*A129860(n). - Andrew Howroyd, Dec 14 2020

PROG

(PARI) my(N=30); U(N, 2) - 2*U(N, 1) \\ See A339650 for U(n, k). - Andrew Howroyd, Dec 14 2020

CROSSREFS

Column 2 of A339650.