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A079987
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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={-1,0,2}.
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0
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1, 0, 0, 1, 2, 3, 5, 7, 15, 29, 49, 84, 149, 268, 484, 855, 1508, 2684, 4784, 8516, 15134, 26873, 47782, 85004, 151149, 268704, 477685, 849299, 1510163, 2685089, 4773851, 8487625, 15090786, 26831239, 47705352, 84818268, 150803857, 268125092
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OFFSET
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0,5
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COMMENTS
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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={-2,0,1}.
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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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LINKS
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Index entries for linear recurrences with constant coefficients, signature (2, -2, 3, -2, 4, -1, -2, 4, -5, 4, -6, 3, 0, -2, 1, -2, 2, -1).
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FORMULA
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a(n) = 2*a(n-1) -2*a(n-2) +3*a(n-3) -2*a(n-4) +4*a(n-5) -a(n-6) -2*a(n-7) +4*a(n-8) -5*a(n-9) +4*a(n-10) -6*a(n-11) +3*a(n-12) -2*a(n-14) +a(n-15) -2*a(n-16) +2*a(n-17) -a(n-18).
G.f.: -(x^12-2*x^11 +2*x^10-2*x^9 +2*x^8-x^7 -x^6+3*x^5 -2*x^4+2*x^3 -2*x^2+2*x -1)/( x^18 -2*x^17 +2*x^16 -x^15 +2*x^14 -3*x^12 +6*x^11 -4*x^10 +5*x^9 -4*x^8 +2*x^7 +x^6 -4*x^5 +2*x^4 -3*x^3 +2*x^2 -2*x+1)
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MATHEMATICA
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LinearRecurrence[{2, -2, 3, -2, 4, -1, -2, 4, -5, 4, -6, 3, 0, -2, 1, -2, 2, -1}, {1, 0, 0, 1, 2, 3, 5, 7, 15, 29, 49, 84, 149, 268, 484, 855, 1508, 2684}, 40] (* Harvey P. Dale, Apr 29 2011 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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