This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A115594 #3 Mar 25 2023 22:40:55 %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. %K A115594 hard,nonn,tabl %O A115594 1,8 %A A115594 David E Speyer (speyer(AT)post.harvard.edu), Mar 09 2006