A005328 Certain subgraphs of a directed graph.

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

Offset: 2

Author

N. J. A. Sloane

Keywords

• nonn

References

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

Links

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

Programs

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

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

Extensions

More terms from Emeric Deutsch, Jan 23 2005