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Search: id:A011781
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| A011781 |
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Sextuple factorial numbers: product[ k=0..n-1 ] (6*k+3). |
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+0
5
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| 1, 3, 27, 405, 8505, 229635, 7577955, 295540245, 13299311025, 678264862275, 38661097149675, 2435649120429525, 168059789309637225, 12604484198222791875, 1020963220056046141875, 88823800144876014343125
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Total number of Eulerian circuits in rooted labeled multigraphs with n edges. - Valery A. Liskovets (liskov(AT)im.bas-net.by), Apr 07 2002
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REFERENCES
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V. A. Liskovets, A note on the total number of Eulerian circuits in multigraphs. In press.
B.Lass, D'emonstration combinatoire de la formule de Harer-Zagier, C. R. Acad. Sci. Paris, Serie I, 333 (2001) No 3, 155-160.
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LINKS
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Valery Liskovets, A Note on the Total Number of Double Eulerian Circuits in Multigraphs , Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.5
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FORMULA
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E.g.f. (1-6*x)^(-1/2).
a(n) = 3^n*(2*n-1)!!.
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PROGRAM
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(PARI) a(n)=if(n<0, 0, (3/2)^n*(2*n)!/n!)
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CROSSREFS
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Cf. A001147, A047657, A049308.
Cf. A069736.
Sequence in context: A078532 A067000 A138436 this_sequence A094577 A108525 A136719
Adjacent sequences: A011778 A011779 A011780 this_sequence A011782 A011783 A011784
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KEYWORD
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nonn
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AUTHOR
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killough(AT)wagner.convex.com (Lee D. Killough)
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