1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor.

A211035

1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor.

Terms

    a(0) =1a(1) =4a(2) =40a(3) =800a(4) =33432a(5) =2888696a(6) =517902680a(7) =192533704008

External references