

A242951


Number of ternary squarefree words x of length n for which some selfshuffle of x is also squarefree.


0



0, 0, 6, 6, 12, 18, 30, 42, 36, 54, 138, 168, 234
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OFFSET

1,3


COMMENTS

"squarefree" means it contains no block of the form xx, with x nonempty. A length2n word w is in the selfshuffle of a lengthn 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, Squarefree 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



