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A139756
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Binomial transform of A004526.
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5
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0, 0, 1, 4, 12, 32, 80, 192, 448, 1024, 2304, 5120, 11264, 24576, 53248, 114688, 245760, 524288, 1114112, 2359296, 4980736, 10485760, 22020096, 46137344, 96468992, 201326592, 419430400, 872415232, 1811939328, 3758096384
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OFFSET
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0,4
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COMMENTS
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Let S be a subset of {1,2,...,n}. A succession in S is a subset of the form {i,i+1}. a(n) is the total number of successions in all subsets of {1,2,...,n}. a(n) = Sum_{k=1,2,...} A076791(n,k)*k. - Geoffrey Critzer, Mar 18 2012.
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REFERENCES
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I Goulden and D Jackson, Combinatorial Enumeration, John Wiley and Sons, 1983, page 55.
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LINKS
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FORMULA
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O.g.f.: x^2/(1-2*x)^2. a(n) = (n-1)*2^n/4 if n>0. - R. J. Mathar, May 22 2008
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EXAMPLE
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a(4) = 12 because we have {1,2}, {2,3}, {3,4}, {1,2,4}, {1,3,4} with one succession; {1,2,3}, {2,3,4} with two successions; and {1,2,3,4} with three successions. - Geoffrey Critzer, Mar 18 2012.
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MATHEMATICA
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nn = 30; a = 1/(1 - y x); b = x/(1 - y x) + 1; c = 1/(1 - x); CoefficientList[ D[Series[c b/(1 - (a x^2 c)), {x, 0, nn}], y] /. y -> 1, x] (*Geoffrey Critzer, Mar 18 2012*)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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