A221256 Number of 2 X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2.

0, 4, 8, 81, 392, 2500, 14112, 83521, 484128, 2829124, 16473800, 96059601, 559785800, 3262922884, 19017180288, 110841719041, 646029804672, 3765346202500, 21946028005832, 127910874833361, 745519107896648

Offset: 1

Author

R. H. Hardin, Jan 06 2013

Keywords

• nonn

Comments

Row 2 of A221255.

Examples

			Some solutions for n=3:
  0 2 2   1 2 0   0 2 1   0 2 1   0 2 0   1 2 0   1 2 1
  0 2 0   0 2 1   0 2 1   1 2 0   1 2 1   1 2 0   0 2 0
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..41

Crossrefs

Cf. A221255.

Formula

Empirical: a(n) = 6*a(n-1) + 6*a(n-2) - 42*a(n-3) + 42*a(n-5) - 6*a(n-6) - 6*a(n-7) + a(n-8).

Empirical g.f.: x^2*(4 - 16*x + 9*x^2 + 26*x^3 - 2*x^4 - 6*x^5 + x^6) / ((1 - x)*(1 + x)*(1 - 6*x + x^2)*(1 + 2*x - x^2)*(1 - 2*x - x^2)). - Colin Barker, Aug 04 2018