1,4

Or, number of labeled 2-connected graphs with n nodes.

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 9.

S. Selkow, Discr. Math. 185 (1998), 183-191.

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

R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.20(b), g(n).

R. W. Robinson, Table of n, a(n) for n = 1..25

Huantian Cao, AutoGF: An Automated System to Calculate Coefficients of Generating Functions.

Harary and Palmer give e.g.f. in Eqn. (1.3.3) on page 10.

Cf. A002218, A004115. Row sums of triangle A123534.

Sequence in context: A012240 A096331 A159497 this_sequence A006423 A067423 A156443

Adjacent sequences: A013919 A013920 A013921 this_sequence A013923 A013924 A013925

nonn,easy,nice

Stanley Selkow (sms(AT)owl.WPI.EDU)