A115594 Triangle read by rows: number of isomorphism classes of series-parallel matroids of rank d on n elements.

1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 3, 4, 3, 1, 1, 4, 8, 8, 4, 1, 1, 5, 14, 19, 14, 5, 1

Offset

1,8

Comments

Slow Mathematica program to list all isomorphism classes for given (d,n) available from author, e-mail speyer(AT)post.harvard.edu.

References

Chapter 6 of Theory of Matroids, edited by N. White. Encyclopedia of Mathematics and its Applications, 26. Cambridge University Press, Cambridge, 1986

Links

Table of n, a(n) for n=1..28.

Example

Triangle begins:
  1
  1 1
  1 1 1
  1 2 2 1
  1 3 4 3 1
  1 4 8 8 4 1
  1 5 14 19 14 5 1
There are 4 series parallel matroids with 6 edges and rank 3:
the four-gon with two edges doubled, the four-gon with one edge tripled,
the four-gon with one diagonal drawn in and one edge doubled,
the four-gon with the diagonal drawn in and doubled.

Crossrefs

Row sums are A001677.

Sequence in context: A122218 A072405 A146565 * A086623 A248736 A292508

Adjacent sequences: A115591 A115592 A115593 * A115595 A115596 A115597

Keyword

hard,nonn,tabl

Author

David E Speyer (speyer(AT)post.harvard.edu), Mar 09 2006

Status

approved