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A140988
Half the number of symmetric n X n binary matrices having equal row sums.
0
1, 2, 5, 20, 139, 1777, 42295, 1888140, 158903233, 25355226287, 7707419775769
OFFSET
1,2
CROSSREFS
Sequence in context: A297630 A297629 A118181 * A136650 A229662 A111885
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jul 28 2008
STATUS
approved