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Search: id:A079986
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| A079986 |
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Number of permutations satisfying -k<=p(i)-i<=r and p(i)-i not in I, i=1..n, with k=3, r=3, I={-2,0,2}. |
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+0
1
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| 1, 0, 1, 0, 4, 0, 16, 0, 49, 0, 169, 0, 576, 0, 1936, 0, 6561, 0, 22201, 0, 75076, 0, 254016, 0, 859329, 0, 2907025, 0, 9834496, 0, 33269824, 0, 112550881, 0, 380757169, 0, 1288092100, 0, 4357584144, 0, 14741602225
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OFFSET
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0,5
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COMMENT
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a(n)=( A000073(k+2) )^2 if n=2k, a(n)=0 otherwise.
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REFERENCES
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D. H. Lehmer, Permutations with strongly restricted displacements. Combinatorial theory and its applications, II (Proc. Colloq., Balatonfured, 1969), pp. 755-770. North-Holland, Amsterdam, 1970.
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FORMULA
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Recurrence: a(n) = 2*a(n-2)+3*a(n-4)+6*a(n-6)-a(n-8)-a(n-12) G.f.: -(x^6+x^4+x^2-1)/(x^12+x^8-6*x^6-3*x^4-2*x^2+1)
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CROSSREFS
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Cf. A002524-A002529, A072827, A072850-A072856, A079955-A080014.
Sequence in context: A081162 A095367 A059065 this_sequence A134746 A003195 A086262
Adjacent sequences: A079983 A079984 A079985 this_sequence A079987 A079988 A079989
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KEYWORD
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nonn
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AUTHOR
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Vladimir Baltic (baltic(AT)galeb.etf.bg.ac.yu), Feb 17 2003
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