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Search: id:A080007
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| A080007 |
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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={0,1}. |
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+0
1
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| 1, 0, 0, 1, 2, 4, 4, 8, 19, 32, 56, 97, 180, 336, 592, 1064, 1925, 3488, 6312, 11345, 20486, 37028, 66852, 120688, 217767, 393216, 710032, 1281729, 2313896, 4177216, 7541568, 13615344, 24579657, 44374528, 80111088, 144628065, 261102474
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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)+4*a(n-5)-2*a(n-7)-a(n-8)-a(n-10) G.f.: -(x^5+x^3+x^2-1)/(x^10+x^8+2*x^7-4*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.
Adjacent sequences: A080004 A080005 A080006 this_sequence A080008 A080009 A080010
Sequence in context: A047073 A069753 A089887 this_sequence A006967 A122033 A096189
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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 10 2003
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