A cubefree word contains no cubed words as subwords. The number of binary cubefree words of length ,
2, ... are 2, 4, 6, 10, 16, 24, 36, 56, 80, 118, ... (OEIS A028445).
Binary cubefree words satisfy
The number of ternary cubefree words of length , 2, ... are 3, 9, 24, 66, 180, 486, 1314, ... (OEIS A051042).
The number of quaternary cubefree words of length , 2, ... are 4, 16, 60, 228, 864, 3264, 12336, ... (OEIS
A051043).
Allouche, J.-P. and Shallit, J. "Repetition in Words." §1.6 in Automatic
Sequences: Theory, Applications, Generalizations. Cambridge, England: Cambridge
University Press, pp. 14-16, 2003.Finch, S. R. "Pattern-Free
Word Constants." §5.17 in Mathematical
Constants. Cambridge, England: Cambridge University Press, pp. 367-371,
2003.Sloane, N. J. A. Sequences A028445,
A051042, and A051043
in "The On-Line Encyclopedia of Integer Sequences."