A strongly connected digraph is a directed graph in which it is possible to reach any node starting from any other node by traversing
edges in the direction(s) in which they point. The nodes in a strongly connected
digraph therefore must all have indegree of at least
1. The numbers of nonisomorphic simple strongly connected digraphs on , 2, ... nodes are 1, 1, 5, 83, 5048, 1047008, ... (OEIS
A035512).
Harary, F. and Palmer, E. M. Graphical Enumeration. New York: Academic Press, p. 218, 1973.Liskovec,
V. A. "A Contribution to the Enumeration of Strongly Connected Digraphs."
Dokl. AN BSSR17, 1077-1080, 1973.Read, R. C. and
Wilson, R. J. An
Atlas of Graphs. Oxford, England: Oxford University Press, 1998.Skiena,
S. "Strong and Weak Connectivity." §5.1.2 in Implementing
Discrete Mathematics: Combinatorics and Graph Theory with Mathematica. Reading,
MA: Addison-Wesley, pp. 94 and 172-174, 1990.Sloane, N. J. A.
Sequence A035512 in "The On-Line Encyclopedia
of Integer Sequences."