0,4

Counts simple matroids, which necessarily cannot have loops or parallel elements.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

J. E. Blackburn, H. H. Crapo and D. A. Higgs, A catalogue of combinatorial geometries, Math. Comp., 27 (1973), 155-166.

Crapo, Henry H.; Rota, Gian-Carlo; On the foundations of combinatorial theory. II. Combinatorial geometries. Studies in Appl. Math. 49 1970 109-133.

W. M. B. Dukes, Tables of matroids

W. M. B. Dukes, Counting and Probability in Matroid Theory, Ph.D. Thesis, Trinity College, Dublin, 2000.

Gordon Royle and Dillon Mayhew, 9-element matroids

N. J. A. Sloane, Initial terms (* denotes 5 points in general position in 4-space)

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Index entries for sequences related to matroids

Cf. A055545, A056642. Row sums of A058730.

Sequence in context: A087378 A004252 A114957 this_sequence A112706 A110138 A148085

Adjacent sequences: A002770 A002771 A002772 this_sequence A002774 A002775 A002776

nonn,nice

N. J. A. Sloane (njas(AT)research.att.com).

a(9) from Gordon Royle, Dec 23 2006