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

A211046

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

Terms

    a(0) =1a(1) =5a(2) =40a(3) =516a(4) =10632a(5) =351016a(6) =18493208a(7) =1556661888a(8) =208981813872

External references