A005328 Certain subgraphs of a directed graph. (Formerly M3118)

1, 3, 28, 510, 18631, 1351413, 194192398, 55272612720, 31184369778961, 34909296450535023, 77616063417393956368, 343049603717222441078130, 3016429354620114423122804491, 52801416275268069417410827891833

Offset

2,2

References

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Table of n, a(n) for n=2..15.

E. Andresen, K. Kjeldsen, On certain subgraphs of a complete transitively directed graph, Discrete Math. 14 (1976), no. 2, 103-119.

Formula

a(n) = p(n-1)*Sum_{j=0..n-2} (-1)^j*(n-1-j)/p(j), where p(0)=1, p(k) = Product_{i=1..k} (2^i - 1) for k > 0. - Emeric Deutsch, Jan 23 2005

Maple

p:=proc(n) if n=0 then 1 else product(2^i-1, i=1..n) fi end: a:=n->p(n-1)*sum((-1)^j*(n-1-j)/p(j), j=0..n-2): seq(a(n), n=2..17); # Emeric Deutsch, Jan 23 2005

Crossrefs

Sequence in context: A327336 A355473 A180710 * A192559 A161971 A156315

Adjacent sequences: A005325 A005326 A005327 * A005329 A005330 A005331

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from Emeric Deutsch, Jan 23 2005

Status

approved