A001677 -id:A001677 - cp's OEIS frontend

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

Original entry on oeis.org

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

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

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

			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.

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

Row sums are A001677.

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