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A174076
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Number of permutations of length n with no consecutive triples i,i+2,i+4 or i,i-2,i-4.
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3
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OFFSET
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5,1
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COMMENTS
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Note for n<5 there are no such subsequences, so those values are trivially n!. Also note it is possible for a permutation to have both i,i+2,i+4 and i,i-2,i-4 triples, as in an example from n=7: (2,4,6,5,3,1,0). This permutation is not counted by a(7).
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LINKS
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Table of n, a(n) for n=5..9.
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EXAMPLE
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For n=5 there are 5!-a(5)=12 permutations with i,i+2,i+4 or i,i-2,i-4 triples. An examples of one is (4,2,0,1,3).
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CROSSREFS
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Cf. A095816, A174077, A174078, A174079.
Sequence in context: A160919 A129027 A204276 * A202194 A203373 A184201
Adjacent sequences: A174073 A174074 A174075 * A174077 A174078 A174079
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KEYWORD
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nonn
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AUTHOR
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Isaac Lambert, Mar 10 2010
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STATUS
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approved
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