https://mathworld.wolfram.com/CubefreeWord.html
Cubefree Word -- from Wolfram MathWorld
A cubefree word contains no cubed words as subwords. The number of binary cubefree words of length n=1, 2, ... are 2, 4, 6, 10, 16, 24, 36, 56, 80, 118, ......
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