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A103943
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Number of unrooted two-vertex n-edge maps in the plane (planar with a distinguished outside face).
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2
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1, 3, 12, 48, 196, 798, 3248, 13184, 53416, 216018, 872344, 3518496, 14177528, 57080572, 229657792, 923474944, 3711572176, 14911097514, 59883185096, 240416320928, 964947251544, 3872021946532, 15533828715232, 62306843932928
(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
| 2a(n)=2^(2n-1)-binomial(2n-1, n-1)+binomial(n-1, floor(n/2)).
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MATHEMATICA
| f[n_] := (2^(2n - 1) - Binomial[2n - 1, n - 1] + Binomial[n - 1, Floor[n/2]])/2; Table[ f[n], {n, 24}] (from Robert G. Wilson v Mar 24 2005)
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CROSSREFS
| Cf. A060404, A033504.
Sequence in context: A002001 A164346 A113956 * A165328 A142873 A151168
Adjacent sequences: A103940 A103941 A103942 * A103944 A103945 A103946
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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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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 24 2005
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