Half the number of n X n binary matrices, symmetric about the diagonal and under 90-degree rotation, having equal row sums.
A140879
Half the number of n X n binary matrices, symmetric about the diagonal and under 90-degree rotation, having equal row sums.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =5a(6) =1a(7) =20a(8) =1a(9) =139a(10) =1a(11) =1777a(12) =1a(13) =42295a(14) =1a(15) =1888140a(16) =1a(17) =158903233a(18) =1a(19) =25355226287a(20) =1a(22) =1
External references
- oeis: A140879