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A014844
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a(n) = 2^n - n*(n-1)/2.
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3
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1, 2, 3, 5, 10, 22, 49, 107, 228, 476, 979, 1993, 4030, 8114, 16293, 32663, 65416, 130936, 261991, 524117, 1048386, 2096942, 4194073, 8388355, 16776940, 33554132, 67108539, 134217377, 268435078, 536870506, 1073741389, 2147483183
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OFFSET
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0,2
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COMMENTS
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a(n) is the number of subsets of {1,2,...,n} that do not have a cardinality of 2. - Geoffrey Critzer, Feb 25 2012
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LINKS
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FORMULA
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G.f.: (1-3*x+2*x^2+x^3)/((1-x)^3*(1-2*x)). - Colin Barker, Apr 01 2012
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MATHEMATICA
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nn = 20; Range[0, nn]! CoefficientList[Series[Exp[x] (Exp[x] - x^2/2!), {x, 0, nn}], x] (* Geoffrey Critzer, Feb 25 2012 *)
CoefficientList[Series[(1-3*x+2*x^2+x^3)/((1-x)^3*(1-2*x)), {x, 0, 33}], x] (* Vincenzo Librandi, Apr 18 2012 *)
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PROG
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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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STATUS
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approved
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