2,3

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

P. Steinbach, Field Guide to Simple Graphs. Design Lab, Albuquerque NM, 1990.

Table of n, a(n) for n=2..7.

Sequence in context: A236409 A000250 A118601 * A121138 A074508 A143500

Adjacent sequences:  A005140 A005141 A005142 * A005144 A005145 A005146

nonn

N. J. A. Sloane.

approved