

A292207


Number of unrooted unlabelled bipartite cubic maps on a compact closed oriented surface with 2*n vertices (and thus 3*n edges).


0



2, 3, 16, 133, 1440, 22076, 401200, 8523946, 206375088, 5611089408, 169259764912, 5610386295418, 202710195084400, 7929759557219228, 333909047017798272, 15059194651009154172, 724232293050284717248
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OFFSET

0,1


COMMENTS

Equivalently, the number of unrooted bicolored triangulations with 2*n triangles (and thus 3*n edges).
Equivalently, the number of pairs of permutations (alpha,sigma) up to simultaneous conjugacy on a set of size 3*n with alpha^3=sigma^3=1, acting transitively and without fixed points.
There is no recurrence relation known for this sequence.


LINKS

Table of n, a(n) for n=0..16.
L. Ciobanu, A. Kolpakov, Free subgroups of free products and combinatorial hypermaps, arXiv:1708.03842 [math.CO], 2017.


CROSSREFS

Unrooted version of A292187.
Sequence in context: A067848 A269067 A139802 * A063666 A006247 A052318
Adjacent sequences: A292204 A292205 A292206 * A292208 A292209 A292210


KEYWORD

nonn


AUTHOR

Sasha Kolpakov, Sep 11 2017


STATUS

approved



