

A001928


Number of connected topologies with n unlabeled nodes.
(Formerly M1655 N0648)


3



1, 1, 2, 6, 21, 94, 512, 3485, 29515, 314474, 4255727, 73831813, 1653083021, 47941962135, 1803010446411, 87882300251730, 5543501326580737
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OFFSET

0,3


REFERENCES

K. K.H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th SE Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169184.
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).
J. A. Wright, There are 718 6point topologies, quasiorderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70TA106.
J. A. Wright, personal communication.


LINKS

Table of n, a(n) for n=0..16.
K. K.H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th SE Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169184
K. K.H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th SE Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169184. [Annotated scan of pages 180 and 183 only]
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
Henry Sharp, Jr., Quasiorderings and topologies on finite sets, Proceedings of the American Mathematical Society 17.6 (1966): 13441349. [Annotated scanned copy]
N. J. A. Sloane, List of sequences related to partial orders, circa 1972
J. A. Wright, There are 718 6point topologies, quasiorderings and transgraphs, Preprint, 1970 [Annotated scanned copy]
J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences


FORMULA

Inverse Euler transform of A001930.  Vladeta Jovovic, Jan 06 2006


CROSSREFS

Cf. A001929, A001930.
Sequence in context: A266328 A214087 A183950 * A005638 A249395 A008988
Adjacent sequences: A001925 A001926 A001927 * A001929 A001930 A001931


KEYWORD

nonn,more


AUTHOR

N. J. A. Sloane.


EXTENSIONS

More terms from Vladeta Jovovic, Jan 06 2006


STATUS

approved



