A208409 Number of 2 X n 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than two of its immediate leftward or upward or right-upward antidiagonal neighbors.

2, 15, 182, 2698, 41914, 658450, 10370330, 163422914, 2575668586, 40595679634, 639841707002, 10084768380770, 158949607034890, 2505261257850802, 39486313909133978, 622357842865595522, 9809203406810575786

Offset: 1

Author

R. H. Hardin, Feb 26 2012

Keywords

• nonn

Comments

Row 2 of A208408.

Examples

			Some solutions for n=4:
..0..0..0..1....0..1..1..1....0..0..0..0....0..0..1..0....0..0..1..0
..1..1..0..0....0..0..0..1....1..0..2..2....0..0..0..0....2..0..1..2
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Cf. A208408.

Formula

Empirical: a(n) = 18*a(n-1) - 31*a(n-2) - 66*a(n-3) - 24*a(n-4) for n>6.

Empirical g.f.: x*(1 + x)*(2 - 23*x - 3*x^2 + 22*x^3 + 8*x^4) / ((1 - 3*x - 2*x^2)*(1 - 15*x - 12*x^2)). - Colin Barker, Jul 02 2018