A248456 Number of length n+2 0..3 arrays with no three consecutive terms having the sum of any two elements equal to twice the third.

48, 148, 460, 1436, 4488, 14040, 43940, 137532, 430508, 1347652, 4218704, 13206360, 41341772, 129418260, 405137308, 1268262348, 3970233208, 12428621208, 38907193300, 121797075276, 381279818252, 1193577924020, 3736437636672

Offset: 1

Author

R. H. Hardin, Oct 06 2014

Keywords

• nonn

Examples

			Some solutions for n=6:
..0....0....0....1....0....2....2....2....2....3....3....1....2....2....0....2
..3....1....3....1....3....3....1....0....3....0....3....1....2....2....3....2
..1....3....1....3....3....0....1....3....3....3....1....0....3....0....2....1
..3....3....3....0....1....0....3....0....2....0....1....1....0....2....0....1
..1....1....0....0....0....3....1....2....3....1....2....0....3....3....0....2
..3....0....3....3....3....3....3....3....3....0....1....0....0....0....2....2
..1....1....0....0....1....0....1....0....2....3....2....2....0....3....0....1
..1....3....2....1....0....0....3....0....2....0....2....2....1....0....2....1
		

Links

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

Crossrefs

Column 3 of A248461.

Formula

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

Empirical g.f.: 4*x*(12 + 13*x + 5*x^2 - 30*x^3 - 53*x^4 - 16*x^5) / (1 - 2*x - 3*x^2 - 4*x^3 + 3*x^4 + 12*x^5 + 4*x^6). - Colin Barker, Nov 08 2018