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A143203
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Numbers having exactly two distinct prime factors p, q with q=p+4.
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5
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21, 63, 77, 147, 189, 221, 437, 441, 539, 567, 847, 1029, 1323, 1517, 1701, 2021, 2873, 3087, 3757, 3773, 3969, 4757, 5103, 5929, 6557, 7203, 8303, 9261, 9317, 9797, 10051, 11021, 11907, 12317, 15309, 16637, 21609
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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MATHEMATICA
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dpf2Q[n_]:=Module[{fi=FactorInteger[n][[;; , 1]]}, Length[fi]==2&&fi[[2]]-fi[[1]]==4]; Select[Range[22000], dpf2Q] (* Harvey P. Dale, Mar 18 2023 *)
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PROG
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(Haskell)
a143203 n = a143203_list !! (n-1)
a143203_list = filter f [1, 3..] where
f x = length pfs == 2 && last pfs - head pfs == 4 where
pfs = a027748_row x
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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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