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

A211050

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

Terms

    a(0) =0a(1) =1a(2) =1a(3) =11a(4) =69a(5) =1059a(6) =21565a(7) =767763a(8) =42018069a(9) =3765457981a(10) =536609175439

External references