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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=0..10.

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.

Cf. A333164, A333166.

Sequence in context: A305292 A268211 A246280 * A133004 A321602 A175169

Adjacent sequences:  A333162 A333163 A333164 * A333166 A333167 A333168

KEYWORD

nonn,more

AUTHOR

Andrew Howroyd, Mar 11 2020

STATUS

approved

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Last modified September 27 19:34 EDT 2021. Contains 347694 sequences. (Running on oeis4.)