%I A115594
%S A115594 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
%N A115594 Triangle read by rows: number of isomorphism classes of series-parallel 
               matroids of rank d on n elements.
%C A115594 Slow Mathematica program to list all isomorphism classes for given (d,
               n) available from author, e-mail speyer(AT)post.harvard.edu.
%D A115594 Chapter 6 of Theory of Matroids, edited by N. White. Encyclopedia of 
               Mathematics and its Applications, 26. Cambridge University Press, 
               Cambridge, 1986
%e A115594 Triangle begins:
%e A115594 1
%e A115594 1 1
%e A115594 1 1 1
%e A115594 1 2 2 1
%e A115594 1 3 4 3 1
%e A115594 1 4 8 8 4 1
%e A115594 1 5 14 19 14 5 1
%e A115594 There are 4 series parallel matroids with 6 edges and rank 3:
%e A115594 the four-gon with two edges doubled, the four-gon with one edge tripled,
%e A115594 the four-gon with one diagonal drawn in and one edge doubled,
%e A115594 the four-gon with the diagonal drawn in and doubled.
%Y A115594 Row sums are A001677.
%Y A115594 Sequence in context: A122218 A072405 A146565 this_sequence A086623 A034928 
               A161671
%Y A115594 Adjacent sequences: A115591 A115592 A115593 this_sequence A115595 A115596 
               A115597
%K A115594 hard,nonn,tabl
%O A115594 1,8
%A A115594 David E Speyer (speyer(AT)post.harvard.edu), Mar 09 2006