A215070 Number of squarefree words of length n in an n-ary alphabet, with new values 0..n-1 introduced in increasing order.

1, 1, 2, 4, 12, 40, 154, 660, 3114, 15930, 87645, 514851, 3211220, 21166029, 146849903, 1068808441, 8136559688, 64621235409, 534207882566

Offset

1,3

Comments

Diagonal of A215075.

Links

Table of n, a(n) for n=1..19.

Example

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

Crossrefs

Sequence in context: A268010 A215073 A215074 * A188479 A062962 A033472

Adjacent sequences: A215067 A215068 A215069 * A215071 A215072 A215073

Keyword

nonn

Author

R. H. Hardin, Aug 02 2012

Status

approved