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    On the maximal number of cubic subwords in a string

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    We investigate the problem of the maximum number of cubic subwords (of the form wwwwww) in a given word. We also consider square subwords (of the form wwww). The problem of the maximum number of squares in a word is not well understood. Several new results related to this problem are produced in the paper. We consider two simple problems related to the maximum number of subwords which are squares or which are highly repetitive; then we provide a nontrivial estimation for the number of cubes. We show that the maximum number of squares xxxx such that xx is not a primitive word (nonprimitive squares) in a word of length nn is exactly ⌊n2βŒ‹βˆ’1\lfloor \frac{n}{2}\rfloor - 1, and the maximum number of subwords of the form xkx^k, for kβ‰₯3k\ge 3, is exactly nβˆ’2n-2. In particular, the maximum number of cubes in a word is not greater than nβˆ’2n-2 either. Using very technical properties of occurrences of cubes, we improve this bound significantly. We show that the maximum number of cubes in a word of length nn is between (1/2)n(1/2)n and (4/5)n(4/5)n. (In particular, we improve the lower bound from the conference version of the paper.)Comment: 14 page
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