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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,3

REFERENCES

R. H. Jeurissen and Th. Bezembinder, Enumerating oriented triangle graphs, Ars Comb. 42(1996), 151-160.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 2..30

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

Adjacent sequences:  A051588 A051589 A051590 * A051592 A051593 A051594

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

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Last modified August 11 20:13 EDT 2022. Contains 356067 sequences. (Running on oeis4.)