A245945 Number of length n+3 0..2 arrays with some pair in every consecutive four terms totalling exactly 2.

71, 197, 545, 1501, 4145, 11441, 31577, 87161, 240581, 664051, 1832917, 5059221, 13964475, 38544783, 106391413, 293661867, 810566283, 2237327253, 6175476757, 17045567707, 47049222251, 129865390965, 358454804639, 989407924729

Offset: 1

Author

R. H. Hardin, Aug 08 2014

Keywords

• nonn

Examples

			Some solutions for n=8:
..0....1....1....1....2....1....0....0....1....1....2....1....0....0....1....2
..1....1....2....1....0....2....2....1....0....2....0....0....0....1....1....0
..2....2....0....2....1....0....2....0....2....2....0....1....2....1....0....0
..0....1....0....0....1....1....0....2....0....1....2....2....0....0....1....1
..1....2....1....1....1....0....2....1....0....0....2....1....1....2....1....2
..0....1....1....0....1....1....2....0....1....1....0....0....0....2....1....1
..2....2....1....2....2....1....1....0....1....2....2....1....1....1....2....0
..2....0....1....2....1....0....0....1....0....2....0....0....2....0....1....2
..0....1....0....0....2....0....1....1....0....0....2....2....0....2....2....0
..0....1....1....1....0....2....1....2....2....2....2....1....2....0....1....0
..2....2....1....1....0....2....2....1....2....1....1....0....0....0....2....2
		

Links

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

Crossrefs

Column 2 of A245950.

Formula

Empirical: a(n) = 2*a(n-1) + 2*a(n-2) + a(n-3) - a(n-4) - 2*a(n-5) - 2*a(n-6) - a(n-7) + a(n-8) + a(n-9).

Empirical g.f.: x*(71 + 55*x + 9*x^2 - 54*x^3 - 73*x^4 - 57*x^5 - 15*x^6 + 36*x^7 + 27*x^8) / ((1 - x)*(1 - x - 3*x^2 - 4*x^3 - 3*x^4 - x^5 + x^6 + 2*x^7 + x^8)). - Colin Barker, Nov 05 2018