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A001200
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Number of linear geometries on n (unlabeled) points.
(Formerly M0726 N0271)
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12
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1, 1, 1, 2, 3, 5, 10, 24, 69, 384, 5250, 232929, 28872973
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,4
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COMMENTS
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Also a(n) = 1 + number of non-isomorphic simple rank-3 matroids on n elements (see A058731); a(n) = number of non-isomorphic 2-partitions of a set of size n. For 1-partitions see A000041.
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REFERENCES
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L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 303, #42.
CRC Handbook of Combinatorial Designs, 1996, pp. 216, 697.
J. Doyen, Sur le nombre d'espaces linéaires non isomorphes de n points. Bull. Soc. Math. Belg. 19 1967 421-437.
P. Robillard, On the weighted finite linear spaces. Bull. Soc. Math. Belg. 22 (1970), 227-241.
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).
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LINKS
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Robert Haas, Cographs, arXiv:1905.12627 [math.GM], 2019.
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CROSSREFS
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KEYWORD
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nonn,hard,more,nice
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AUTHOR
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EXTENSIONS
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Dead link to Betten paper replaced with CiteSeer entry (which has full text as cached PDF) Robert Munafo, Dec 13 2009
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STATUS
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approved
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