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A140217 Half the number of n X n binary matrices, symmetric under horizontal reflection, having equal row sums. 1
1, 1, 2, 9, 34, 730, 4376, 905345, 10601986, 10009765626, 200097656252, 2177748514672962, 85812416258106784, 4142789042980129347156, 289904403212517959978240, 175519033940460517461369847809 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

R. H. Hardin, Jul 28 2008, Table of n, a(n) for n = 1..25

CROSSREFS

Sequence in context: A276901 A151308 A215943 * A182407 A284550 A200050

Adjacent sequences:  A140214 A140215 A140216 * A140218 A140219 A140220

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 28 2008

STATUS

approved

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Last modified May 15 18:26 EDT 2021. Contains 343920 sequences. (Running on oeis4.)