4,2

Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, p. 403.

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.

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

R. W. Robinson, Table of n, a(n) for n = 4..25

T. R. S. Walsh, Counting labeled three-connected and homeomorphically irreducible two-connected graphs, J. Combin. Theory Ser. B 32 (1982), no. 1, 1-11.

Row sums of A123542.

Sequence in context: A080163 A300578 A217228 * A123537 A220503 A054597

Adjacent sequences: A005641 A005642 A005643 * A005645 A005646 A005647

nonn

N. J. A. Sloane.

Corrected and extended by N. J. A. Sloane, Nov 13 2006

approved