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A112946
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Number of unrooted regular odd-valent planar maps with 6 vertices; maps are considered up to orientation-preserving homeomorphisms and the vertices are of valency 2n+1.
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3
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0, 26, 111096, 513654400, 2243178389200, 9550256850912960, 40141310067406592352, 167483578096089845880576, 695587719666862982630642400, 2880023438585172541459822939200
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OFFSET
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0,2
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COMMENTS
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There is a closed formula.
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LINKS
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MATHEMATICA
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a[n_] := With[{b = Binomial[2n, n]}, (1/120)(36n-1) n^2 b^6 + (3n^2 b^3)/4 + n b^2/3 + (4/5) Boole[Divisible[2n+1, 5]] Binomial[2 Floor[n/5], Floor[n/5]] b];
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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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