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A140884 Half the number of n X n binary matrices, symmetric under 90-degree rotation, having equal row sums. 0
1, 1, 1, 4, 3, 13, 43, 580, 1897, 23851, 149041, 14348161, 74552521, 7849966951, 311500453881, 64690704744716, 2466747100788601, 493809829542170401 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..18.

CROSSREFS

Sequence in context: A088933 A019136 A298057 * A351992 A082383 A216486

Adjacent sequences:  A140881 A140882 A140883 * A140885 A140886 A140887

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 28 2008

STATUS

approved

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Last modified May 23 07:19 EDT 2022. Contains 353961 sequences. (Running on oeis4.)