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%I #15 Apr 13 2017 03:23:16
%S 1,2,4,14,140,4322,434542,144109562,165431317452,654143160457922,
%T 9331115832294448754,469229841129645179004962,
%U 87481268294773501231007850158,58328998963405322376273800187396962,147013017541698957281403494604070439260442
%N Number of n X n 0..1 matrices with all row and column sums equal.
%H Alois P. Heinz, <a href="/A067209/b067209.txt">Table of n, a(n) for n = 0..30</a>
%H E. R. Canfield and B. D. McKay, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v12i1r29">Asymptotic enumeration of dense 0-1 matrices with equal row and column sums</a>
%H B. D. McKay, <a href="http://users.cecs.anu.edu.au/~bdm/data/semiregular.html">0-1 matrices with constant row and column sums</a>
%e Some solutions for n=5
%e ..1..1..0..0..1....0..0..1..0..1....0..1..0..1..1....1..1..0..1..0
%e ..1..1..0..0..1....1..1..0..0..0....1..1..0..0..1....1..0..1..1..0
%e ..0..0..1..1..1....1..0..0..1..0....1..1..1..0..0....1..0..1..0..1
%e ..1..0..1..1..0....0..1..1..0..0....0..0..1..1..1....0..1..0..1..1
%e ..0..1..1..1..0....0..0..0..1..1....1..0..1..1..0....0..1..1..0..1
%Y Row sums of A008300.
%K nonn
%O 0,2
%A _R. H. Hardin_, Feb 20 2002
%E Added one term and example - _R. H. Hardin_, Jan 05, 2012
%E a(0)=1 prepended and more terms (using data provided by B. D. McKay) from _Alois P. Heinz_, Apr 12 2017
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