1,2

a(n) appears to be [A060639(n) + 1] / 2. - Ralf Stephan, Aug 21 2004

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

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

E. N. Gilbert, Enumeration of labeled graphs, Canad. J. Math., 8 (1956), 405-411.

D. G. Cantor, personal communication.

Sequence in context: A001415 A053871 A052622 this_sequence A113145 A036794 A096121

Adjacent sequences: A001185 A001186 A001187 this_sequence A001189 A001190 A001191

nonn

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