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 A333165 #5 Mar 14 2020 18:54:09
%S A333165 1,1,2,5,66,7937,10211144,133506398361,18551599312980440,
%T A333165 28652629505982770906471,510824181488832447063505273252
%N A333165 Number of non-isomorphic 2n X 2n symmetric matrices with entries in {+1, -1} and all rows and columns summing to zero.
%C A333165 a(n) is the number of non-isomorphic 2n X 2n symmetric binary matrices with n ones in every row and column.
%F A333165 a(n) = A333159(2*n, n).
%e A333165 The a(1) = 1 matrix is:
%e A333165 [+ -]
%e A333165 [- +]
%e A333165 The a(2) = 2 matrices are:
%e A333165 [+ + - -] [+ + - -]
%e A333165 [+ + - -] [+ - + -]
%e A333165 [- - + +] [- + - +]
%e A333165 [- - + +] [- - + +]
%Y A333165 Central coefficients of A333159.
%Y A333165 Cf. A333164, A333166.
%K A333165 nonn,more
%O A333165 0,3
%A A333165 _Andrew Howroyd_, Mar 11 2020