A246478 Number of length n+3 0..7 arrays with no pair in any consecutive four terms totalling exactly 7.

1880, 10376, 57416, 317576, 1756472, 9714968, 53733080, 297195272, 1643773832, 9091640072, 50285457464, 278126631896, 1538306048600, 8508302434184, 47059042885064, 260281476168584, 1439605284832568, 7962392893359512

Offset: 1

Author

R. H. Hardin, Aug 27 2014

Keywords

• nonn

Examples

			Some solutions for n=3:
..5....0....1....0....2....4....6....0....2....5....6....7....2....7....7....7
..7....5....0....1....6....0....5....4....1....3....2....3....0....3....6....4
..5....6....1....4....7....1....6....1....7....1....6....6....3....3....4....7
..5....6....5....2....6....0....7....0....1....7....7....5....6....1....5....4
..5....0....0....2....2....2....6....0....5....7....6....5....5....2....4....7
..1....6....1....6....3....4....2....3....1....5....2....5....3....7....4....5
		

Links

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

Crossrefs

Column 7 of A246479.

Formula

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

Empirical g.f.: 8*x*(235 + 122*x + 222*x^2 + 43*x^3) / (1 - 5*x - 2*x^2 - 5*x^3 - x^4). - Colin Barker, Nov 06 2018