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A246536
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a(n) = number of strings (including the empty string) over an alphabet of size n that do not have any substrings of length > 1 that appear more than once in the string.
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0
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OFFSET
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1,1
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COMMENTS
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Here "substrings" have no "gaps", i.e. a substring means a subsequence of characters from the original string using contiguous indices.
The number of De Bruijn sequences B(n,2) (which has a known explicit formula) can be used to give the fairly tight lower bound that a(n) > 2*n^2*B(n,2). See A166315.
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LINKS
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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