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A006473
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a(n) = binomial(n,2)!/n!.
(Formerly M5217)
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1
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1, 30, 30240, 1816214400, 10137091700736000, 7561714896123855667200000, 1025113885554181044609786839040000000, 32964677266721834921175915315161407370035200000000, 318071672921132854486459356650996997744817246158245068800000000000
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OFFSET
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3,2
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COMMENTS
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a(n) is also the number of distinct possible (n-1)-dimensional simplices if the (n-1)*n/2 1-faces are given (up to symmetry, rotation, reflection). - Dan Dima, Nov 03 2011
a(n) is also the number of edge labelings of the complete graph on n vertices. - Nikos Apostolakis, Jul 09 2013
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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EXAMPLE
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a(3)=1 since there is one possible triangle if the 3 edges are given and a(4)=30 since there are 30 distinct possible tetrahedra if the 6 edges are given. - Dan Dima, Nov 03 2011
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MATHEMATICA
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Table[Binomial[n, 2]!/n!, {n, 3, 20}] (* Harvey P. Dale, May 08 2013 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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