A246473 Number of length n+3 0..2 arrays with no pair in any consecutive four terms totalling exactly 2.

10, 14, 20, 28, 38, 52, 72, 100, 138, 190, 262, 362, 500, 690, 952, 1314, 1814, 2504, 3456, 4770, 6584, 9088, 12544, 17314, 23898, 32986, 45530, 62844, 86742, 119728, 165258, 228102, 314844, 434572, 599830, 827932, 1142776, 1577348, 2177178

Offset: 1

Author

R. H. Hardin, Aug 27 2014

Keywords

• nonn

Comments

Column 2 of A246479.

Examples

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

Links

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

Crossrefs

Cf. A246479.

Formula

Empirical: a(n) = a(n-1) + a(n-4).

Empirical g.f.: 2*x*(5 + 2*x + 3*x^2 + 4*x^3) / (1 - x - x^4). - Colin Barker, Mar 19 2018