0,4

For the labeled case see A056642.

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.

Blackburn et al., A catalogue of combinatorial geometries, Math. Comp 27 1973 155-166.

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 lineaires non isomorphes de n points. Bull. Soc. Math. Belg. 19 1967 421-437.

D. G. Glynn, Rings of geometries II, J. Combin. Theory, A 49 (1988), 26-66.

D. G. Glynn, A geometrical isomorphism algorithm, Bull. ICA 7 (1993), 36-38.

Ch. Pietsch, On the classification of linear spaces of order 11, J. Comb. Designs, 3 (1995), 185-193.

P. Robillard, On the weighted finite linear spaces. Bull. Soc. Math. Belg. 22 (1970), 227-241.

A. Betten and D. Betten, Linear spaces with at most 12 points, J. Combinatorial Designs, Volume 7, 1999, pp. 119 - 145.

Cf. A000041, A056642, A058731.

Sequence in context: A106531 A101163 A125658 this_sequence A050837 A107578 A011827

Adjacent sequences: A001197 A001198 A001199 this_sequence A001201 A001202 A001203

nonn,hard,nice

njas, D.Glynn(AT)math.canterbury.ac.nz