A215224 Number of length-n 0..4 arrays connected end-around, with no sequence of L<n elements immediately followed by itself (periodic "squarefree").

5, 20, 60, 240, 720, 2940, 10080, 38640, 140400, 529440, 1956900, 7335840, 27285180, 101960040, 380209980, 1419732000

Offset

1,1

Comments

Column 4 of A215228.

Links

Table of n, a(n) for n=1..16.

Example

Some solutions for n=8:
..2....2....1....4....4....3....3....1....0....0....1....1....4....4....4....4
..3....4....4....0....0....1....4....3....4....1....4....3....0....2....2....1
..2....0....3....2....4....2....2....4....1....0....3....0....3....3....1....3
..0....4....1....3....3....0....1....3....3....3....1....4....2....2....4....0
..1....3....2....4....0....1....3....0....2....2....3....3....1....1....0....3
..2....0....3....3....1....3....2....2....4....0....0....0....4....0....2....1
..4....2....0....1....0....0....0....4....3....1....3....2....3....2....0....0
..0....1....3....2....2....2....1....2....2....3....2....4....2....0....3....2

Crossrefs

Sequence in context: A327383 A339588 A344099 * A270939 A270631 A032340

Adjacent sequences: A215221 A215222 A215223 * A215225 A215226 A215227

Keyword

nonn,more

Author

R. H. Hardin, Aug 06 2012

Status

approved