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A112945
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Number of unrooted regular odd-valent planar maps with 4 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, 6, 468, 80600, 16016560, 3360790440, 728936019504, 161858688461184, 36580777518027600, 8382066029146609800, 1941971956789550319920, 454006489072843947528288, 106944132919124515725427808
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OFFSET
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0,2
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LINKS
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Table of n, a(n) for n=0..12.
Z. C. Gao, V. A. Liskovets and N. C. Wormald, Enumeration of unrooted odd-valent regular planar maps, Preprint, 2005.
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FORMULA
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a(n)=(n/6)binomial(2n, n)^4+(n/2)binomial(2n, n)^2+(2/3)delta(3|(2n+1))* binomial(2*floor(n/3), floor(n/3))*binomial(2n, n) where delta(3|(2n+1))=1 if 3|(2n+1) and =0 otherwise.
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CROSSREFS
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Cf. A112944, A112946.
Sequence in context: A051735 A024084 A132590 * A220865 A080295 A084108
Adjacent sequences: A112942 A112943 A112944 * A112946 A112947 A112948
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KEYWORD
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nonn
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AUTHOR
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Valery A. Liskovets, Oct 10 2005
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STATUS
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approved
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