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, 28 August, 2000.
R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).