A140879 - OEIS

A140879

Half the number of n X n binary matrices, symmetric about the diagonal and under 90-degree rotation, having equal row sums.

%I #5 Nov 25 2018 13:56:21

%S 1,1,1,2,1,5,1,20,1,139,1,1777,1,42295,1,1888140,1,158903233,1,

%T 25355226287,1,7707419775769,1

%N Half the number of n X n binary matrices, symmetric about the diagonal and under 90-degree rotation, having equal row sums.

%K nonn

%O 1,4

%A _R. H. Hardin_, Jul 28 2008