A221567 Number of 0..2 arrays of length n with each element differing from at least one neighbor by something other than 1.

0, 5, 9, 25, 57, 141, 345, 853, 2097, 5149, 12633, 31013, 76161, 187053, 459369, 1128053, 2770065, 6802301, 16704249, 41020357, 100732833, 247366989, 607452297, 1491704341, 3663139761, 8995478557, 22089965337, 54245756261, 133209897153

Offset: 1

Author

R. H. Hardin Jan 20 2013

Keywords

• nonn

Comments

Column 2 of A221573

Examples

			Some solutions for n=6
..2....1....2....0....0....1....2....0....0....0....0....2....0....2....0....1
..0....1....2....0....0....1....0....2....2....0....0....0....0....2....0....1
..0....1....1....2....2....0....0....2....2....2....2....1....2....1....0....2
..0....0....1....2....0....0....0....0....0....0....2....1....2....1....2....2
..2....0....2....2....2....1....1....2....0....0....1....2....2....2....0....0
..0....0....2....2....2....1....1....2....2....2....1....0....0....0....0....2
		

Links

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

Formula

Empirical: a(n) = 3*a(n-1) -2*a(n-2) +4*a(n-4).

Empirical g.f.: -x^2*(5-6*x+8*x^2) / ( -1+3*x-2*x^2+4*x^4 ). - R. J. Mathar, Jun 06 2013