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%I #18 Feb 03 2020 05:55:36
%S 1,9,282,14697,1071750,100467405,11509922970,1558302613245,
%T 243426592473750,43095781327975425,8527098853816839450,
%U 1864790504534293823025,446647359698685492697350,116281255808439040209815925,32694665144001284972518220250
%N Number of unrooted level-2 phylogenetic networks with (n+1) labeled leaves, when multiple (i.e. parallel) edges are allowed.
%H Mathilde Bouvel, Philippe Gambette and Marefatollah Mansouri, <a href="http://user.math.uzh.ch/bouvel/publications/BouvelGambetteMansouri_Version1_WithMultipleEdges.mw">Maple worksheet</a>
%H Mathilde Bouvel, Philippe Gambette and Marefatollah Mansouri, <a href="https://arxiv.org/abs/1909.10460v2">Counting Phylogenetic Networks of level 1 and 2</a>, Version 2, arXiv:1909.10460 [math.CO], 2019.
%F Bouvel, Gambette and Mansouri provide (among other results) a closed formula for a(n), an equation for the associated exponential generating function, and an asymptotic estimate of a(n). See their Section 6.
%e a(3) = 282 is the number of unrooted level-2 phylogenetic networks with 4 labeled leaves.
%p # see links section
%Y Cf. A328121, A328122, A328126.
%K nonn
%O 1,2
%A _Mathilde Bouvel_, Oct 04 2019
%E Name clarified by _Mathilde Bouvel_, Feb 03 2020
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