

A001548


Number of connected linear spaces with n (unlabeled) points.
(Formerly M1270 N0489)


6



1, 1, 0, 1, 1, 2, 4, 13, 42, 308, 4845, 227613, 2653970
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OFFSET

0,6


COMMENTS

Euler transform is A001200.  Michael Somos, Apr 24 2014
In any linear space any two distinct points belong to exactly one line. A linear space is disconnected if there exists a partition of the points of the space into two subsets such that for any two distinct points in a subset of the partition the unique line they both belong to is completely contained in that subset.  Michael Somos, Apr 24 2014


REFERENCES

L. M. Batten and A. Beutelspacher: The theory of finite linear spaces, Cambridge Univ. Press, 1993 (see the Appendix).
Doyen, Jean; Sur le nombre d'espaces lineaires non isomorphes de n points. Bull. Soc. Math. Belg. 19 1967 421437.
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

Table of n, a(n) for n=0..12.
J. Doyen, Sur le nombre d'espaces lineaires non isomorphes de n points [Annotated and scanned copy]
Robillard, Pierre, On the weighted finite linear spaces, Bull. Soc. Math. Belg. 22 (1970), 227241. [Annotated and scanned copy]


EXAMPLE

a(2) = 0 because the unique linear space on two points can be partitioned into two single point subsets which disconnects the space vacuously. a(5) = 2 because there are two connected linear spaces with 5 points: one has only one line and the other has two lines with three points that intersect in one point that belongs to no other line while the other four points belong to three lines.  Michael Somos, Apr 24 2014


CROSSREFS

Cf. A001199, A001200, A056642.
Sequence in context: A284159 A050624 A135501 * A193057 A115600 A007858
Adjacent sequences: A001545 A001546 A001547 * A001549 A001550 A001551


KEYWORD

nonn,hard,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

More terms could be obtained from A056642.  N. J. A. Sloane, Jul 26 2004
a(10)a(12) from A001200.  Michael Somos, Apr 24 2014


STATUS

approved



