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A305759
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Numbers that can be factored as a product of numbers of the form 2^k+1 (A000051).
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0
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1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 17, 18, 20, 24, 25, 27, 30, 32, 33, 34, 36, 40, 45, 48, 50, 51, 54, 60, 64, 65, 66, 68, 72, 75, 80, 81, 85, 90, 96, 99, 100, 102, 108, 120, 125, 128, 129, 130, 132, 135, 136, 144, 150, 153, 160, 162, 165, 170, 180, 192
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OFFSET
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1,2
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COMMENTS
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If a(n) and a(m) are in the sequence, so is a(n)*a(m).
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LINKS
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EXAMPLE
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a(11) = 15 = 3*5 = (2^1 + 1)*(2^2 + 1).
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MATHEMATICA
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up = 192; t = Complement[1+2^Range[0, Ceiling@Log2@up], {9}]; a = {}; ric[p_, w_] := Block[{q = p}, If[w == {}, AppendTo[a, p], While[q <= up, ric[q, Rest@w]; q *= w[[1]]]]]; ric[1, t]; Union[a] (* Giovanni Resta, Jun 14 2018 *)
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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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STATUS
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approved
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