0,3

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

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 218.

R. C. Read (rcread(AT)math.uwaterloo.ca), email to N. J. A. Sloane (njas(AT)research.att.com), 28 August, 2000.

R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.

R. W. Robinson, Counting strong digraphs (research announcement), J. Graph Theory 1, 1977, pp. 189-190.

Cf. A057270, A003029 (labeled case), A003085, A035512, A051421, A049531, A049512.

Sequence in context: A013050 A051255 A120445 this_sequence A121231 A122527 A039747

Adjacent sequences: A003085 A003086 A003087 this_sequence A003089 A003090 A003091

nonn,nice,more

N. J. A. Sloane (njas(AT)research.att.com).

Note that Read and Wilson incorrectly give a(4) as 172 - thanks to Vladeta Jovovic, Goran Kilibarda (vladeta(AT)eunet.rs) for finding this error and for verifying a(5).