A207421 Number of nX3 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 0 1 and 0 1 0 vertically.

6, 36, 114, 351, 1162, 3633, 11067, 33994, 103972, 315900, 959469, 2913192, 8833205, 26769585, 81116398, 245729000, 744251550, 2253989395, 6825832650, 20669704173, 62589261963, 189520870122, 573861525576, 1737611142984, 5261327251049

Offset: 1

Author

R. H. Hardin Feb 17 2012

Keywords

• nonn

Comments

Column 3 of A207426

Examples

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

Links

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

Formula

Empirical: a(n) = 4*a(n-1) -4*a(n-2) +13*a(n-3) -30*a(n-4) +3*a(n-5) -29*a(n-6) +50*a(n-7) +56*a(n-8) +28*a(n-9) -34*a(n-10) -76*a(n-11) -42*a(n-12) +14*a(n-13) +35*a(n-14) +20*a(n-15) +4*a(n-16) -7*a(n-17) -2*a(n-18) -a(n-19) -a(n-20)