

A140417


Half the number of n X n symmetric binary matrices with each 1 adjacent to some 0 horizontally (and vertically) and each 0 adjacent to some 1 horizontally (and vertically).


0



1, 1, 4, 13, 77, 556, 5859, 83423, 1659982, 45479269, 1727097809, 90646136576, 6583459833641, 661303481127357, 91895146207819652, 17663776192483786871
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