A221521 Number of 0..5 arrays of length n with each element differing from at least one neighbor by 2 or more.

0, 20, 68, 400, 1940, 9982, 50400, 256018, 1297924, 6584320, 33394958, 169387004, 859152000, 4357755890, 22103183110, 112110699524, 568642349004, 2884239836106, 14629299498936, 74202014273586, 376363810775194

Offset

1,2

Comments

Column 5 of A221524.

Links

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

Formula

Empirical: a(n) = 2*a(n-1) +11*a(n-2) +20*a(n-3) +17*a(n-4) -3*a(n-5) +a(n-6).

Empirical g.f.: 2*x^2*(10 + 14*x + 22*x^2 - 4*x^3 + x^4) / (1 - 2*x - 11*x^2 - 20*x^3 - 17*x^4 + 3*x^5 - x^6). - Colin Barker, Oct 18 2017

Example

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

Crossrefs

Sequence in context: A158444 A235281 A303620 * A145191 A044158 A044539

Adjacent sequences: A221518 A221519 A221520 * A221522 A221523 A221524

Keyword

nonn

Author

R. H. Hardin, Jan 19 2013

Status

approved