A245864 Number of length n+2 0..2 arrays with some pair in every consecutive three terms totalling exactly 2.

19, 45, 103, 239, 553, 1281, 2967, 6873, 15921, 36881, 85435, 197911, 458463, 1062035, 2460217, 5699123, 13202089, 30582803, 70845443, 164114349, 380172929, 880675315, 2040095313, 4725906149, 10947620333, 25360298571, 58747446847

Offset: 1

Author

R. H. Hardin, Aug 04 2014

Keywords

• nonn

Examples

			Some solutions for n=10:
..1....2....1....2....0....1....0....1....0....0....2....0....0....2....0....0
..1....1....1....2....0....1....2....1....2....1....2....1....0....1....1....1
..1....1....1....0....2....1....1....1....0....1....0....2....2....0....1....1
..1....0....0....2....1....1....1....1....2....2....2....0....0....2....2....0
..1....2....2....0....1....1....1....2....2....0....1....2....2....2....0....1
..0....2....0....1....2....2....0....1....0....1....1....0....1....0....2....2
..2....0....1....1....0....1....2....0....2....1....0....2....1....2....2....0
..2....1....1....1....2....0....0....2....2....1....1....1....1....2....0....1
..0....2....2....1....0....1....0....1....0....1....1....1....0....0....0....1
..2....1....1....0....1....2....2....1....1....1....1....0....1....0....2....0
..2....0....0....1....1....1....0....2....2....2....1....2....1....2....2....1
..0....1....1....1....1....0....2....1....0....1....1....0....2....0....0....2
		

Links

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

Crossrefs

Column 2 of A245869.

Formula

Empirical: a(n) = 2*a(n-1) + a(n-2) - a(n-4) - a(n-5).

Empirical g.f.: x*(19 + 7*x - 6*x^2 - 12*x^3 - 9*x^4) / ((1 - x)*(1 - x - 2*x^2 - 2*x^3 - x^4)). - Colin Barker, Nov 03 2018