

A292206


Number of unrooted unlabeled connected fourregular maps on a compact closed oriented surface with n vertices (and thus 2*n edges).


0



2, 7, 36, 365, 5250, 103801, 2492164, 70304018, 2265110191, 82013270998, 3295691020635, 145553281837454, 7008046130978980, 365354356543414133, 20504381826687810441, 1232562762503125498772, 79012106044626365750974
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OFFSET

0,1


COMMENTS

Equivalently, the number of unrooted quadrangulations of oriented surfaces with n quadrangles (and thus 2*n edges).
Equivalently, the number of pairs of permutations (alpha,sigma) up to simultaneous conjugacy on a set of size 4*n with alpha^2=sigma^4=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 A292186.
Sequence in context: A072236 A007474 A002724 * A203900 A209251 A274904
Adjacent sequences: A292203 A292204 A292205 * A292207 A292208 A292209


KEYWORD

nonn


AUTHOR

Sasha Kolpakov, Sep 11 2017


STATUS

approved



