A140984 - OEIS

%I #7 Mar 09 2015 04:31:33

%S 1,2,4,35,226,7592,156752,22458249,1718157826,941605438142,

%T 250228936146872,572800408273738658,580834777459374862880,

%U 5136409738603278958315040,18792196647668946085817284928

%N Half the number of n X n binary matrices, symmetric under 180 degree rotation, having equal row sums.

%H R. H. Hardin, Jul 28 2008, <a href="/A140984/b140984.txt">Table of n, a(n) for n = 1..25</a>

%K nonn

%O 1,2

%A _R. H. Hardin_, Jul 28 2008