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

1,1

Links

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

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

Example

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

Crossrefs

Column 2 of A245869.

Sequence in context: A140680 A183632 A359558 * A183624 A115249 A325451

Adjacent sequences: A245861 A245862 A245863 * A245865 A245866 A245867

Keyword

nonn

Author

R. H. Hardin, Aug 04 2014

Status

approved