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Search: id:A079981
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| A079981 |
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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={-2,0,1,2}. |
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+0
2
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| 1, 0, 0, 0, 1, 0, 2, 0, 3, 0, 8, 0, 12, 0, 27, 0, 52, 0, 95, 0, 196, 0, 369, 0, 720, 0, 1408, 0, 2709, 0, 5292, 0, 10249, 0, 19894, 0, 38675, 0, 74992, 0, 145692, 0, 282823, 0, 549000, 0, 1066095, 0, 2069496, 0, 4018065, 0, 7801024, 0, 15144960, 0, 29404281, 0
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OFFSET
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0,7
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COMMENT
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Also, 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,-1,0,2}. a(n)=A079980(k) 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) = a(n-4)+4*a(n-6)+2*a(n-8)+2*a(n-10)-2*a(n-12)+a(n-14)+a(n-18) G.f.: -(x^12-2*x^6+1)/(x^18+x^14-2*x^12+2*x^10+2*x^8+4*x^6+x^4-1)
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CROSSREFS
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Cf. A002524-A002529, A072827, A072850-A072856, A079955-A080014.
Adjacent sequences: A079978 A079979 A079980 this_sequence A079982 A079983 A079984
Sequence in context: A076563 A089780 A067165 this_sequence A117776 A137448 A035165
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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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