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A242951 Number of ternary squarefree words x of length n for which some self-shuffle of x is also squarefree. 0
0, 0, 6, 6, 12, 18, 30, 42, 36, 54, 138, 168, 234 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

"squarefree" means it contains no block of the form xx, with x nonempty.  A length-2n word w is in the self-shuffle of a length-n word x if there is a disjoint partition of the indices {1,2,..., 2n} into two increasing sequences of length n, say s and t, such that x = w[s] = w[t].

LINKS

Table of n, a(n) for n=1..13.

T. Harju and M. Mueller, Square-free shuffles of words, arxiv preprint, 2013, Table 3, page 7.

CROSSREFS

Cf. A242949.

Sequence in context: A315794 A315795 A315796 * A022089 A275288 A110357

Adjacent sequences:  A242948 A242949 A242950 * A242952 A242953 A242954

KEYWORD

nonn,more

AUTHOR

Jeffrey Shallit, May 27 2014

STATUS

approved

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Last modified April 18 22:08 EDT 2019. Contains 322237 sequences. (Running on oeis4.)