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A292206
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Number of unrooted unlabeled connected four-regular maps on a compact closed oriented surface with n vertices (and thus 2*n edges).
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0
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2, 7, 36, 365, 5250, 103801, 2492164, 70304018, 2265110191, 82013270998, 3295691020635, 145553281837454, 7008046130978980, 365354356543414133, 20504381826687810441, 1232562762503125498772, 79012106044626365750974
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refs;
listen;
history;
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internal format)
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OFFSET
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0,1
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COMMENTS
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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.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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