A222549 Number of (n+2) X 1 arrays of occupancy after each element moves up to +-2 places but not 0.

7, 20, 64, 208, 651, 2056, 6496, 20483, 64627, 203905, 643272, 2029453, 6402679, 20199560, 63726952, 201050056, 634285971, 2001087460, 6313163200, 19917184799, 62836052203, 198239333473, 625418559696, 1973111833705, 6224903700199

Offset: 1

Author

R. H. Hardin, Feb 24 2013

Keywords

• nonn

Comments

Column 2 of A222555.

Examples

			Some solutions for n=3:
..0....0....0....0....2....0....0....1....0....1....0....1....2....2....1....1
..3....1....2....2....0....1....1....1....0....2....0....1....2....1....0....2
..2....4....1....1....2....2....3....0....3....0....1....0....0....1....1....1
..0....0....2....1....1....0....0....2....1....2....2....1....1....1....1....0
..0....0....0....1....0....2....1....1....1....0....2....2....0....0....2....1
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..147

Crossrefs

Cf. A222555.

Formula

Empirical: a(n) = 5*a(n-1) - 6*a(n-2) + 2*a(n-3) - 8*a(n-4) + 12*a(n-5) - 3*a(n-6) - a(n-7).

Empirical g.f.: x*(7 - 15*x + 6*x^2 - 6*x^3 + 11*x^4 - 3*x^5 - x^6) / ((1 - x)*(1 - 4*x + 2*x^2 + 8*x^4 - 4*x^5 - x^6)). - Colin Barker, Aug 16 2018