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A259116
Number of unrooted binary unordered tanglegrams of size n.
2
1, 1, 1, 2, 4, 22, 145, 1875, 31929, 698183, 18056523, 538340256, 18141423039, 681939320185
OFFSET
1,4
COMMENTS
Binary tanglegrams are pairs of bifurcating (degree 3 internal node) trees with a bijection between the leaves of the trees. Two tanglegrams are isomorphic if there is an isomorphism between the trees that preserves the bijection. Unrooted means that the tanglegram is composed of unrooted trees, and unordered means that two tanglegrams that differ by exchanging the trees and inverting the bijection are considered identical.
LINKS
S. C. Billey, M. Konvalinka, and F. A. Matsen IV, On the enumeration of tanglegrams and tangled chains, arXiv:1507.04976 [math.CO], 2015.
Ira M. Gessel, Counting tanglegrams with species, arXiv:1509.03867 [math.CO], (13-September-2015)
F. A. Matsen IV, S. C. Billey, D. A. Kas, and M. Konvalinka, Tanglegrams: a reduction tool for mathematical phylogenetics, arXiv:1507.04784 [q-bio.PE], 2015.
CROSSREFS
Cf. A258620 (tanglegrams), A259114, A259115, A258486 (tangled chains), A258487, A258488, A258489.
Sequence in context: A321248 A309741 A110130 * A283322 A019025 A264729
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
More terms from Ira M. Gessel, Jul 19 2015
STATUS
approved