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A079976
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Expansion of g.f. 1/(1-x-x^2-x^4-x^5).
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2
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1, 1, 2, 3, 6, 11, 20, 36, 65, 118, 214, 388, 703, 1274, 2309, 4185, 7585, 13747, 24915, 45156, 81841, 148329, 268832, 487232, 883061, 1600463, 2900685, 5257212, 9528190, 17268926, 31298264, 56725087, 102808753, 186330956, 337706899
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OFFSET
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0,3
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COMMENTS
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Number of compositions of n into elements of the set {1,2,4,5}.
Number of permutations (p(1),...,p(n)) of (1..n) satisfying -k<=p(i)-i<=r and p(i)-i not in I, i=1..n, with k=1, r=4, I={2}.
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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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FORMULA
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a(n) = a(n-1)+a(n-2)+a(n-4)+a(n-5).
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MATHEMATICA
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CoefficientList[Series[1/(1-x-x^2-x^4-x^5), {x, 0, 40}], x] (* or *) LinearRecurrence[ {1, 1, 0, 1, 1}, {1, 1, 2, 3, 6}, 40] (* Harvey P. Dale, Mar 16 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Since this sequence arises in several different contexts, I made the definition as simple as possible. - N. J. A. Sloane, Apr 17 2011
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STATUS
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approved
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