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A090375
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Number of unrooted Eulerian maps with bicolored faces which are self-isomorphic under reversing the colors.
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0
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1, 1, 2, 4, 8, 17, 40, 93, 224, 538, 1344, 3352, 8448, 21573, 54912, 143037, 366080, 968083, 2489344, 6664856
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| a(2k+1)= 2^k*Catalan(k)=A052701(k+1)
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LINKS
| V. Liskovets, Some easily derivable integer sequences, J. Integer Seq., v.3 (2000), Article 00.2.2.
V. A. Liskovets, Enumerative formulae for unrooted planar maps: a pattern, Electron. J. Combin., 11:1 (2004), R88.v11i1r88.pdf
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FORMULA
| a(n)=2*A069727(n)-A090371(n)
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CROSSREFS
| Sequence in context: A054199 A054197 A137856 * A104879 A156805 A200542
Adjacent sequences: A090372 A090373 A090374 * A090376 A090377 A090378
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KEYWORD
| easy,nonn
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AUTHOR
| Valery Liskovets (liskov(AT)im.bas-net.by), Dec 01 2003
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