There are ternary circular square-free words of length n for n≥ 18.
Currie, James D.
The Electronic Journal of Combinatorics [electronic only], Tome DS10 (2002), / Harvested from The Electronic Library of Mathematics
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Publié le : 2002-01-01
EUDML-ID : urn:eudml:doc:124300 
@article{01862491,
     title = {There are ternary circular square-free words of length },
     journal = {The Electronic Journal of Combinatorics [electronic only]},
     volume = {DS10},
     year = {2002},
     zbl = {1057.68081},
     language = {en},
     url = {http://dml.mathdoc.fr/item/01862491}
}

Currie, James D. There are ternary circular square-free words of length . The Electronic Journal of Combinatorics [electronic only], Tome DS10 (2002) . http://gdmltest.u-ga.fr/item/01862491/