

A002218


Number of unlabeled nonseparable (or 2connected) graphs (or blocks) with n nodes.
(Formerly M2873 N1155)


13



0, 1, 1, 3, 10, 56, 468, 7123, 194066, 9743542, 900969091, 153620333545, 48432939150704, 28361824488394169, 30995890806033380784, 63501635429109597504951, 244852079292073376010411280, 1783160594069429925952824734641, 24603887051350945867492816663958981
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OFFSET

1,4


COMMENTS

By definition, a(n) counts the number of graphs with zero cutpoints.  Travis Hoppe, Apr 28 2014


REFERENCES

P. Butler and R. W. Robinson, On the computer calculation of the number of nonseparable graphs, pp. 191  208 of Proc. Second Caribbean Conference Combinatorics and Computing (Bridgetown, 1977). Ed. R. C. Read and C. C. Cadogan. University of the West Indies, Cave Hill Campus, Barbados, 1977. vii+223 pp.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 188.
R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.
R. W. Robinson and T. R. S. Walsh, Inversion of cycle index sum relations for 2 and 3connected graphs. J. Combin. Theory Ser. B 57 (1993), no. 2, 289308.
Andrew J. Schultz and David A. Kofke, Fifth to eleventh virial coefficients of hard spheres, Phys. Rev. E 90, 023301, 4 August 2014
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

R. W. Robinson, Table of n, a(n) for n = 1..26
P. Butler and R. W. Robinson, On the computer calculation of the number of nonseparable graphs, pp. 191  208 of Proc. Second Caribbean Conference Combinatorics and Computing (Bridgetown, 1977). Ed. R. C. Read and C. C. Cadogan. University of the West Indies, Cave Hill Campus, Barbados, 1977. vii+223 pp. [Annotated scanned copy]
R. W. Robinson, Computer printout of first 26 terms [Annotated scanned copy]
R. W. Robinson, Tables
R. W. Robinson, Enumeration of nonseparable graphs, J. Combin. Theory 9 (1970), 327356.
R. W. Robinson and T. R. S. Walsh, Inversion of cycle index sum relations for 2 and 3connected graphs, J. Combin. Theory Ser. B. 57 (1993), 289308.
D. Stolee, Isomorphfree generation of 2connected graphs with applications, arXiv preprint arXiv:1104.5261, 2011
Eric Weisstein's World of Mathematics, Biconnected Graph
Eric Weisstein's World of Mathematics, kConnected Graph


CROSSREFS

Cf. A000088, A001349, A006289, A006290, A004115, A013922, A241767.
Sequence in context: A081721 A013009 A203416 * A107871 A111270 A274585
Adjacent sequences: A002215 A002216 A002217 * A002219 A002220 A002221


KEYWORD

nonn,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

More terms from R. C. Read (rcread(AT)math.uwaterloo.ca). Robinson and Walsh list the first 26 terms.


STATUS

approved



