A208873 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 one of its immediate leftward or upward or right-upward antidiagonal neighbors.

2, 12, 136, 1798, 24472, 334618, 4578580, 62655190, 857412640, 11733394642, 160567489036, 2197311225838, 30069453572632, 411490201499818, 5631102858140740, 77059719245016070, 1054535937228511120

Offset: 1

Author

R. H. Hardin, Mar 02 2012

Keywords

• nonn

Comments

Row 2 of A208872.

Examples

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

Links

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

Crossrefs

Cf. A208872.

Formula

Empirical: a(n) = 18*a(n-1) - 65*a(n-2) + 84*a(n-3) - 36*a(n-4) for n>5.

Empirical g.f.: 2*x*(1 - 12*x + 25*x^2 - 19*x^3 + 6*x^4) / ((1 - x)*(1 - 2*x)*(1 - 15*x + 18*x^2)). - Colin Barker, Jul 07 2018