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 A333159 #5 Mar 11 2020 18:06:52 %S A333159 1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,2,2,1,1,1,1,4,5,4,1,1,1,1,4,12,12, %T A333159 4,1,1,1,1,7,31,66,31,7,1,1,1,1,8,90,433,433,90,8,1,1,1,1,12,285,3442, %U A333159 7937,3442,285,12,1,1,1,1,14,938,30404,171984,171984,30404,938,14,1,1 %N A333159 Triangle read by rows: T(n,k) is the number of non-isomorphic n X n symmetric binary matrices with k ones in every row and column up to permutation of rows and columns. %C A333159 Rows and columns may be permuted independently. The case that rows and columns must be permuted together is covered by A333161. %C A333159 T(n,k) is the number of k-regular bicolored graphs on 2n unlabeled nodes which are invariant when the two color classes are exchanged. %H A333159 Andrew Howroyd, <a href="/A333159/b333159.txt">Table of n, a(n) for n = 0..230</a> %F A333159 T(n,k) = T(n,n-k). %e A333159 Triangle begins: %e A333159 1; %e A333159 1, 1; %e A333159 1, 1, 1; %e A333159 1, 1, 1, 1; %e A333159 1, 1, 2, 1, 1; %e A333159 1, 1, 2, 2, 1, 1; %e A333159 1, 1, 4, 5, 4, 1, 1; %e A333159 1, 1, 4, 12, 12, 4, 1, 1; %e A333159 1, 1, 7, 31, 66, 31, 7, 1, 1; %e A333159 1, 1, 8, 90, 433, 433, 90, 8, 1, 1; %e A333159 1, 1, 12, 285, 3442, 7937, 3442, 285, 12, 1, 1; %e A333159 ... %e A333159 The T(2,1) = 1 matrix is: %e A333159 [1 0] %e A333159 [0 1] %e A333159 . %e A333159 The T(4,2)= 2 matrices are: %e A333159 [1 1 0 0] [1 1 0 0] %e A333159 [1 1 0 0] [1 0 1 0] %e A333159 [0 0 1 1] [0 1 0 1] %e A333159 [0 0 1 1] [0 0 1 1] %Y A333159 Columns k=0..4 are A000012, A000012, A002865, A000840, A000843. %Y A333159 Row sums are A333160. %Y A333159 Central coefficients are A333165. %Y A333159 Cf. A008327, A122082, A333157, A133687, A333161. %K A333159 nonn,tabl %O A333159 0,13 %A A333159 _Andrew Howroyd_, Mar 10 2020