OFFSET
0,3
COMMENTS
a(n) is the number of non-isomorphic 2n X 2n symmetric binary matrices with n ones in every row and column.
FORMULA
a(n) = A333159(2*n, n).
EXAMPLE
The a(1) = 1 matrix is:
[+ -]
[- +]
The a(2) = 2 matrices are:
[+ + - -] [+ + - -]
[+ + - -] [+ - + -]
[- - + +] [- + - +]
[- - + +] [- - + +]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Andrew Howroyd, Mar 11 2020
STATUS
approved