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A165964
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Number of circular permutations of length n without increasing or decreasing 3-sequences.
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11
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1, 1, 0, 4, 16, 86, 542, 3932, 32330, 297438, 3028320, 33814454, 410954878, 5400878692, 76329470882, 1154445436334, 18606430004984, 318369275913710, 5764046146341198, 110091446931897180, 2212282487296335866
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OFFSET
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1,4
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COMMENTS
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Circular permutations are permutations whose indices are from the ring of integers modulo n. Increasing 3-sequences are of the form i,i+1,i+2, while decreasing 3-sequences are of the form i,i-1,i-2.
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LINKS
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Table of n, a(n) for n=1..21.
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FORMULA
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a(n) = A095816(n-1) - 2 * Sum{i=1,[n/3], A095816(n-3i) - A095816(n-1-3i)}.
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EXAMPLE
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For n=4 the a(4)=4 solutions are (0,1,3,2), (0,2,1,3), (0,2,3,1), and (0,3,1,2).
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CROSSREFS
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Cf. A095816, A165963, A078628.
Sequence in context: A074876 A238722 A184507 * A005618 A005495 A052124
Adjacent sequences: A165961 A165962 A165963 * A165965 A165966 A165967
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KEYWORD
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nonn
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AUTHOR
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Isaac Lambert, Oct 07 2009
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EXTENSIONS
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Edited and more terms added by Max Alekseyev, Jun 14 2011
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STATUS
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approved
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