A246474 Number of length n+3 0..3 arrays with no pair in any consecutive four terms totalling exactly 3.

60, 132, 292, 644, 1420, 3132, 6908, 15236, 33604, 74116, 163468, 360540, 795196, 1753860, 3868260, 8531716, 18817292, 41502844, 91537404, 201892100, 445287044, 982111492, 2166115084, 4777517212, 10537145916, 23240406916, 51258331044

Offset: 1

Author

R. H. Hardin, Aug 27 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 3 of A246479.

Formula

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

Empirical g.f.: 4*x*(15 + 3*x + 7*x^2) / (1 - 2*x - x^3). - Colin Barker, Nov 06 2018