1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, two, three or four horizontal and vertical neighbors.

A211051

1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, two, three or four horizontal and vertical neighbors.

Terms

    a(0) =1a(1) =5a(2) =45a(3) =801a(4) =27967a(5) =1940165a(6) =265677267a(7) =71849269093

External references