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Search: id:A115594
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| A115594 |
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Triangle read by rows: number of isomorphism classes of series-parallel matroids of rank d on n elements. |
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+0
1
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| 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
(list; table; graph; listen)
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OFFSET
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1,8
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COMMENT
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Slow Mathematica program to list all isomorphism classes for given (d,n) available from author, e-mail speyer(AT)post.harvard.edu.
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REFERENCES
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Chapter 6 of Theory of Matroids, edited by N. White. Encyclopedia of Mathematics and its Applications, 26. Cambridge University Press, Cambridge, 1986
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EXAMPLE
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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.
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CROSSREFS
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Row sums are A001677.
Sequence in context: A047089 A122218 A072405 this_sequence A086623 A034928 A144444
Adjacent sequences: A115591 A115592 A115593 this_sequence A115595 A115596 A115597
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KEYWORD
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hard,nonn,tabl
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AUTHOR
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David E Speyer (speyer(AT)post.harvard.edu), Mar 09 2006
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