A215223 Number of length-n 0..3 arrays connected end-around, with no sequence of L<n elements immediately followed by itself (periodic "squarefree").

4, 12, 24, 72, 120, 408, 840, 2448, 5760, 15960, 39864, 108024, 275184, 728784, 1895760, 4998528, 13033560, 34250904, 89602632, 235157640, 615871032

Offset

1,1

Comments

Column 3 of A215228.

Links

Table of n, a(n) for n=1..21.

Example

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

Crossrefs

Sequence in context: A051193 A356550 A216244 * A318610 A296358 A282512

Adjacent sequences: A215220 A215221 A215222 * A215224 A215225 A215226

Keyword

nonn,more

Author

R. H. Hardin, Aug 06 2012

Status

approved