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A051591 Number of oriented triangle graphs with transitively oriented maximal cliques, on binomial(n,2) points. 1

%I

%S 1,1,18,66360,4147236820,19902009929142960,10325801406739620796634430,

%T 776107138571279347069904891019268480,

%U 10911068841557131648034491574230872615312437194176

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

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

%H Vincenzo Librandi, <a href="/A051591/b051591.txt">Table of n, a(n) for n = 2..30</a>

%F a(n) = Sum_{d|n} { d^d * ( (n-1)! )^d / ( n^d * d!) }, valid for n > 4.

%e n=5: 4!/5 + 5^5*(4!)^5 / (5^5*5!) = 66360.

%t Join[{1, 1, 18},

%t Table[Plus @@

%t Map[Function[d, d^d ((n - 1)!)^d /( (n^d) d!)], Divisors[n]], {n, 5, 8}]]

%o (PARI) a(n) = sumdiv(n, d, d^d * ( (n-1)! )^d / ( n^d * d!) ); \\ for n>4, _Michel Marcus_, Mar 29 2014

%K nonn

%O 2,3

%A R. H. Jeurissen (jeuris(AT)sci.kun.nl)

%E Edited by _Olivier GĂ©rard_, Mar 29 2014

%E Corrected and extended by _Vincenzo Librandi_, Mar 29 2014

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Last modified September 29 01:56 EDT 2022. Contains 357082 sequences. (Running on oeis4.)