A268452 Number of length-n 0..3 arrays with no adjacent pair x,x+1 followed at any distance by x+1,x.

4, 16, 61, 229, 852, 3146, 11536, 42032, 152254, 548568, 1966757, 7019311, 24946486, 88313632, 311507619, 1095064315, 3837407016, 13407618832, 46715533678, 162345449332, 562801287366, 1946559269050, 6717910370343, 23136984979001

Offset: 1

Author

R. H. Hardin, Feb 04 2016

Keywords

• nonn

Comments

Column 3 of A268457.

Examples

			Some solutions for n=9
..0....1....0....1....1....0....3....3....3....2....1....1....2....1....0....2
..1....2....2....0....1....1....0....2....0....2....0....0....0....2....0....2
..2....3....2....2....0....3....3....3....3....3....0....3....0....2....0....2
..3....0....0....2....2....0....0....3....3....0....2....3....1....0....2....2
..1....2....1....3....0....0....1....1....1....0....0....3....2....0....0....3
..3....3....3....3....0....2....3....3....1....1....1....1....2....3....0....1
..1....3....0....0....2....1....1....1....0....3....1....3....2....0....1....2
..2....0....0....2....0....1....1....1....0....3....3....1....3....0....2....0
..0....3....2....2....0....2....2....3....0....0....0....0....0....3....3....1
		

Links

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

Crossrefs

Cf. A268457.

Formula

Empirical: a(n) = 19*a(n-1) -156*a(n-2) +730*a(n-3) -2178*a(n-4) +4446*a(n-5) -6613*a(n-6) +7587*a(n-7) -6948*a(n-8) +5152*a(n-9) -3101*a(n-10) +1503*a(n-11) -573*a(n-12) +163*a(n-13) -31*a(n-14) +3*a(n-15)