A267465 Number of length-n 0..2 arrays with no following elements larger than the first repeated value.

3, 9, 24, 62, 160, 418, 1112, 3018, 8352, 23522, 67240, 194554, 568304, 1672146, 4946808, 14692970, 43767616, 130647490, 390566216, 1168815066, 3500415888, 10488664754, 31439779864, 94264813642, 282681194720, 847808703138

Offset: 1

Author

R. H. Hardin, Jan 15 2016

Keywords

• nonn

Comments

Column 2 of A267471.

Examples

			Some solutions for n=7:
..2....1....2....1....2....2....1....1....1....0....1....0....0....1....1....2
..1....0....1....0....1....2....2....0....1....1....2....1....1....2....2....2
..0....2....0....1....0....2....0....1....0....0....2....1....2....2....1....1
..1....2....1....0....1....0....1....2....1....1....1....0....1....2....0....1
..2....2....2....2....1....1....0....2....1....0....0....0....0....1....1....2
..2....0....1....0....0....0....2....1....1....1....0....0....1....2....2....2
..1....2....2....1....0....1....0....1....1....0....1....0....1....0....2....2
		

Links

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

Crossrefs

Cf. A267471.

Formula

Empirical: a(n) = 8*a(n-1) -23*a(n-2) +28*a(n-3) -12*a(n-4).

Conjectures from Colin Barker, Feb 05 2018: (Start)

G.f.: x*(3 - 15*x + 21*x^2 - 7*x^3) / ((1 - x)*(1 - 2*x)^2*(1 - 3*x)).

a(n) = 2^n + 3^(n-1) + 2^(n-2)*(n+1) - 1.

(End)