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A000608
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Number of connected partially ordered sets with n unlabeled elements.
(Formerly M2864 N1152)
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5
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1, 1, 1, 3, 10, 44, 238, 1650, 14512, 163341, 2360719, 43944974, 1055019099, 32664984238, 1303143553205, 66900392672168, 4413439778321689
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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REFERENCES
| K. K.-H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th S-E Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169-184.
G. Melan\c{c}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 6-point topologies, quasi-orderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70T-A106.
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LINKS
| Gunnar Brinkmann and Brendan D. McKay, Counting unlabeled topologies and transitive relations.
G. Brinkmann, B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147-179
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
N. J. A. Sloane, Transforms
Index entries for sequences related to posets
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CROSSREFS
| Inverse Euler transform of A000112.
Sequence in context: A096804 A113059 A167995 * A205803 A009648 A007125
Adjacent sequences: A000605 A000606 A000607 * A000609 A000610 A000611
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KEYWORD
| hard,nonn,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe, J. A. Wright
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EXTENSIONS
| More terms from Christian Bower (bowerc(AT)usa.net), who pointed out connection with A000112, Jan 21 1998 and Dec 12 2001
More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 04 2006; corrected Jan 15 2006
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