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A333165
Number of non-isomorphic 2n X 2n symmetric matrices with entries in {+1, -1} and all rows and columns summing to zero.
3
1, 1, 2, 5, 66, 7937, 10211144, 133506398361, 18551599312980440, 28652629505982770906471, 510824181488832447063505273252
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
Central coefficients of A333159.
Sequence in context: A305292 A268211 A246280 * A374674 A133004 A321602
KEYWORD
nonn,more
AUTHOR
Andrew Howroyd, Mar 11 2020
STATUS
approved