

A000608


Number of connected partially ordered sets with n unlabeled elements.
(Formerly M2864 N1152)


5



1, 1, 1, 3, 10, 44, 238, 1650, 14512, 163341, 2360719, 43944974, 1055019099, 32664984238, 1303143553205, 66900392672168, 4413439778321689
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OFFSET

0,4


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.
E. N. Gilbert, A catalog of partially ordered systems, unpublished memorandum, Aug 08, 1961.
G. MelanĂ§on, personal communication.
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.


LINKS

Table of n, a(n) for n=0..16.
Gunnar Brinkmann and Brendan D. McKay, Counting unlabeled topologies and transitive relations.
G. Brinkmann and B. D. McKay, Counting unlabeled topologies and transitive relations, J. Integer Sequences, Volume 8, 2005.
G. Brinkmann and B. D. McKay, Posets on up to 16 Points [On Brendan McKay's home page]
G. Brinkmann, B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147179
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.
E. N. Gilbert, A catalog of partially ordered systems, unpublished memorandum, Aug 08, 1961. [Annotated scanned copy]
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
N. J. A. Sloane, Transforms
Peter Steinbach, Field Guide to Simple Graphs, Volume 4, Part 10 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
N. L. White, Two letters to N. J. A. Sloane, 1970, with handdrawn enclosure
J. A. Wright, There are 718 6point topologies, quasiorderings and transgraphs, Preprint, 1970 [Annotated scanned copy]
J. A. Wright, Two related abstracts, 1970 and 1972 [Annotated scanned copies]
J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences
Index entries for sequences related to posets


CROSSREFS

Inverse Euler transform of A000112.
Sequence in context: A113059 A240172 A167995 * A259352 A205803 A009648
Adjacent sequences: A000605 A000606 A000607 * A000609 A000610 A000611


KEYWORD

hard,more,nonn,nice


AUTHOR

N. J. A. Sloane, Simon Plouffe, J. A. Wright


EXTENSIONS

More terms from Christian G. Bower, who pointed out connection with A000112, Jan 21 1998 and Dec 12 2001
More terms from Vladeta Jovovic, Jan 04 2006; corrected Jan 15 2006


STATUS

approved



