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A103939
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Number of unrooted Eulerian n-edge maps in the plane (planar with a distinguished outside face).
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1
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1, 3, 8, 32, 136, 722, 3924, 22954, 138316, 860364, 5472444, 35503288, 234070648, 1564945158, 10589356592, 72412611194, 499788291616, 3478059566250, 24383023246284, 172074483068320
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| V. A. Liskovets and T. R. Walsh, Enumeration of unrooted maps on the plane, Rapport technique, UQAM, No. 2005-01, Montreal, Canada, 2005.
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LINKS
| V. A. Liskovets and T. R. Walsh, Counting unrooted maps on the plane, Advances in Applied Math., 36, No.4 (2006), 364-387.
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FORMULA
| a(n)=(1/(2n))[2^n*binomial(2n, n)/(n+1) + sum_{0<k<n, k|n}phi(n/k)2^k*binomial(2k, k)] where phi is the Euler function A000010.
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CROSSREFS
| Cf. A052701, A103940, A069727.
Sequence in context: A148915 A151541 A022563 * A094610 A064316 A009438
Adjacent sequences: A103936 A103937 A103938 * A103940 A103941 A103942
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KEYWORD
| easy,nonn
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AUTHOR
| Valery A. Liskovets (liskov(AT)im.bas-net.by), Mar 17 2005
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