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A195106
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Numbers with largest and smallest prime factors differing by 4.
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3
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21, 63, 77, 105, 147, 189, 221, 315, 437, 441, 525, 539, 567, 735, 847, 945, 1029, 1323, 1517, 1575, 1701, 2021, 2205, 2625, 2835, 2873, 3087, 3675, 3757, 3773, 3969, 4725, 4757, 5103, 5145, 5929, 6557, 6615, 7203, 7875, 8303, 8505, 9261, 9317, 9797, 10051
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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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a(10) = 441 = 3^2 * 7^2;
a(11) = 525 = 3 * 5^2 * 7;
a(12) = 539 = 7^2 * 11.
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MATHEMATICA
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pf4Q[n_]:=Module[{pfs=Transpose[FactorInteger[n]][[1]]}, Max[pfs]- Min[pfs]==4]; Select[Range[11000], pf4Q] (* Harvey P. Dale, Sep 24 2011 *)
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PROG
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(Haskell)
a195106 n = a195106_list !! (n-1)
a195106_list = filter (\x -> a006530 x - a020639 x == 4) [1, 3..]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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