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 A067209 Number of n X n 0..1 matrices with all row and column sums equal. 4
 1, 2, 4, 14, 140, 4322, 434542, 144109562, 165431317452, 654143160457922, 9331115832294448754, 469229841129645179004962, 87481268294773501231007850158, 58328998963405322376273800187396962, 147013017541698957281403494604070439260442 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..30 E. R. Canfield and B. D. McKay, Asymptotic enumeration of dense 0-1 matrices with equal row and column sums B. D. McKay, 0-1 matrices with constant row and column sums EXAMPLE Some solutions for n=5 ..1..1..0..0..1....0..0..1..0..1....0..1..0..1..1....1..1..0..1..0 ..1..1..0..0..1....1..1..0..0..0....1..1..0..0..1....1..0..1..1..0 ..0..0..1..1..1....1..0..0..1..0....1..1..1..0..0....1..0..1..0..1 ..1..0..1..1..0....0..1..1..0..0....0..0..1..1..1....0..1..0..1..1 ..0..1..1..1..0....0..0..0..1..1....1..0..1..1..0....0..1..1..0..1 CROSSREFS Row sums of A008300. Sequence in context: A102897 A305856 A001527 * A134040 A061291 A166105 Adjacent sequences:  A067206 A067207 A067208 * A067210 A067211 A067212 KEYWORD nonn AUTHOR R. H. Hardin, Feb 20 2002 EXTENSIONS Added one term and example - R. H. Hardin, Jan 05, 2012 a(0)=1 prepended and more terms (using data provided by B. D. McKay) from Alois P. Heinz, Apr 12 2017 STATUS approved

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Last modified December 5 20:41 EST 2019. Contains 329777 sequences. (Running on oeis4.)