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).
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).
Terms
- a(0) =1a(1) =1a(2) =4a(3) =13a(4) =77a(5) =556a(6) =5859a(7) =83423a(8) =1659982a(9) =45479269a(10) =1727097809a(11) =90646136576
External references
- oeis: A140417