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A263866
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Number of permutations of [n] with no carrier element, that is, having their exterior (longest pattern that is both a proper prefix and a proper suffix) contained in their interior (permutation obtained by deleting the first and the last entry) as a consecutive pattern.
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0
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OFFSET
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2,2
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LINKS
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EXAMPLE
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For n=3, we have a(3)=4 because the permutations 132, 213, 231, 312 have exterior equal to 1, and thus contained in their interior. On the other hand, 123 has exterior 12, and 321 has exterior 21.
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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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