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Search: id:A080006
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| A080006 |
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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=2, r=3, I={0,2}. |
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+0
1
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| 1, 0, 1, 1, 3, 5, 8, 16, 27, 51, 91, 164, 298, 536, 972, 1755, 3172, 5735, 10363, 18735, 33861, 61204, 110628, 199957, 361427, 653277, 1180800, 2134300, 3857748, 6972892, 12603513, 22780876, 41176481, 74426569, 134526179, 243156337
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OFFSET
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0,5
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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) = a(n-2)+2*a(n-3)+2*a(n-4)+3*a(n-5)+a(n-6)-a(n-8)-a(n-9)-a(n-10) G.f.: -(x^5+x^3-1)/(x^10+x^9+x^8-x^6-3*x^5-2*x^4-2*x^3-x^2+1)
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CROSSREFS
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Cf. A002524-A002529, A072827, A072850-A072856, A079955-A080014.
Sequence in context: A099846 A141775 A056765 this_sequence A112656 A002366 A141615
Adjacent sequences: A080003 A080004 A080005 this_sequence A080007 A080008 A080009
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KEYWORD
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nonn
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AUTHOR
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Vladimir Baltic (baltic(AT)matf.bg.ac.yu), Feb 10 2003
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