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A051591
Number of oriented triangle graphs with transitively oriented maximal cliques, on binomial(n,2) points.
1
1, 1, 18, 66360, 4147236820, 19902009929142960, 10325801406739620796634430, 776107138571279347069904891019268480, 10911068841557131648034491574230872615312437194176
OFFSET
2,3
REFERENCES
R. H. Jeurissen and Th. Bezembinder, Enumerating oriented triangle graphs, Ars Comb. 42(1996), 151-160.
LINKS
FORMULA
a(n) = Sum_{d|n} { d^d * ( (n-1)! )^d / ( n^d * d!) }, valid for n > 4.
EXAMPLE
n=5: 4!/5 + 5^5*(4!)^5 / (5^5*5!) = 66360.
MATHEMATICA
Join[{1, 1, 18},
Table[Plus @@
Map[Function[d, d^d ((n - 1)!)^d /( (n^d) d!)], Divisors[n]], {n, 5, 8}]]
PROG
(PARI) a(n) = sumdiv(n, d, d^d * ( (n-1)! )^d / ( n^d * d!) ); \\ for n>4, Michel Marcus, Mar 29 2014
CROSSREFS
Sequence in context: A079303 A159445 A146548 * A146203 A192081 A290177
KEYWORD
nonn
AUTHOR
R. H. Jeurissen (jeuris(AT)sci.kun.nl)
EXTENSIONS
Edited by Olivier Gérard, Mar 29 2014
Corrected and extended by Vincenzo Librandi, Mar 29 2014
STATUS
approved