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A100819
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Composite numbers whose prime factors are twin primes.
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1
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9, 15, 21, 25, 27, 33, 35, 39, 45, 49, 51, 55, 57, 63, 65, 75, 77, 81, 85, 87, 91, 93, 95, 99, 105, 117, 119, 121, 123, 125, 129, 133, 135, 143, 145, 147, 153, 155, 165, 169, 171, 175, 177, 183, 187, 189, 195, 203, 205, 209, 213, 215, 217, 219, 221
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OFFSET
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1,1
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LINKS
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EXAMPLE
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221 = 13 * 17 (13 is the twin prime of 11 and 17 is the twin prime to 19).
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MATHEMATICA
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nn = 100; p = Prime[Range[nn]]; t = {}; Do[If[p[[n + 1]] - p[[n]] == 2 || p[[n]] - p[[n - 1]] == 2, AppendTo[t, p[[n]]]], {n, nn - 1}]; Select[Range[2, t[[-1]]], ! PrimeQ[#] && Complement[Transpose[FactorInteger[#]][[1]], t] == {} &] (* T. D. Noe, May 21 2013 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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New name, typo in example fixed by Zak Seidov, May 20 2013
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STATUS
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approved
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