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A143205
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Numbers having exactly two distinct prime factors p, q with q=p+6.
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4
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55, 91, 187, 247, 275, 391, 605, 637, 667, 1147, 1183, 1375, 1591, 1927, 2057, 2491, 3025, 3127, 3179, 3211, 4087, 4459, 4693, 4891, 5767, 6647, 6655, 6875, 7387, 8281, 8993, 9991, 10807, 11227, 12091, 15125, 15341, 15379, 17947, 19343, 22627, 23707
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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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Eric Weisstein's World of Mathematics, Sexy Primes. [The definition in this webpage is unsatisfactory, because it defines a "sexy prime" as a pair of primes.- N. J. A. Sloane, Mar 07 2021]
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EXAMPLE
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MATHEMATICA
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okQ[n_]:=Module[{fi=Transpose[FactorInteger[n]][[1]]}, Length[fi]==2 && Last[fi]-First[fi]==6]; Select[Range[25000], okQ] (* Harvey P. Dale, Apr 18 2011 *)
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PROG
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(Haskell)
a143205 n = a143205_list !! (n-1)
a143205_list = filter f [1, 3..] where
f x = length pfs == 2 && last pfs - head pfs == 6 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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