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Search: id:A089973
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| A089973 |
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Number of maximum-length 2-surprising sequences in n symbols. |
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+0
2
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OFFSET
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1,2
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COMMENT
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A sequence of symbols is 2-surprising if, for every pair of symbols X and Y, not necessarily distinct, and every distance D, there is at most one position in t he sequence where X precedes Y by distance D. The maximum lengths are given in A0899 72.
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REFERENCES
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Dennis E. Shasha, Puzzling Adventures, Scientific American 289(#12, 2003), 22.
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EXAMPLE
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The 2-surprising sequences in 3 symbols are:
(2012100) (1021200) (1120210) (2011210) (1202210) (2210120) (2101120) (1022120)
(2100201) (0021201) (0212201) (2102011) (0120211) (2010021) (2201021) (0122021)
(1200102) (0121102) (0012102) (1020012) (0211012) (1102012) (1201022) (0210122)
Thus a(3)=24.
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CROSSREFS
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Cf. A008062.
Sequence in context: A000056 A083170 A087081 this_sequence A033581 A009943 A028595
Adjacent sequences: A089970 A089971 A089972 this_sequence A089974 A089975 A089976
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KEYWORD
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nonn
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AUTHOR
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John W. Layman (layman(AT)math.vt.edu), Nov 17 2003
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