A051591 Number of oriented triangle graphs with transitively oriented maximal cliques, on binomial(n,2) points.

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

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