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

1,2

LINKS

Table of n, a(n) for n=1..11.

CROSSREFS

Sequence in context: A297630 A297629 A118181 * A136650 A229662 A111885

Adjacent sequences:  A140985 A140986 A140987 * A140989 A140990 A140991

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 28 2008

STATUS

approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)