A207094 Number of 0..2 arrays x(0..n-1) of n elements with each no smaller than the sum of its two previous neighbors modulo 3.

3, 6, 12, 26, 55, 115, 239, 498, 1038, 2162, 4502, 9375, 19523, 40655, 84659, 176292, 367107, 764456, 1591886, 3314907, 6902887, 14374415, 29932954, 62331700, 129798109, 270288619, 562842849, 1172051097, 2440652442, 5082358916

Offset: 1

Author

R. H. Hardin, Feb 15 2012

Keywords

• nonn

Comments

Column 2 of A207100.

Examples

			Some solutions for n=5:
..1....0....1....0....0....0....0....0....1....0....1....1....0....0....0....0
..2....1....2....1....1....0....0....2....1....0....2....2....1....1....0....0
..2....1....1....1....2....0....2....2....2....0....1....2....2....2....0....0
..1....2....1....2....2....0....2....1....2....1....0....1....1....1....0....0
..2....2....2....0....1....1....2....2....2....2....1....0....2....0....0....2
		

Links

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

Crossrefs

Cf. A207100.

Formula

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

Empirical g.f.: x*(3 + 2*x^3 - x^5 - x^8) / ((1 - x)*(1 - x - x^2 - x^3 - 2*x^4 - 2*x^5 - x^6 - x^7 - x^8)). - Colin Barker, Jun 18 2018