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A177211
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Numbers k that are the products of two distinct primes such that 2*k-1 and 4*k-3 are also products of two distinct primes.
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11
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33, 118, 119, 134, 146, 226, 247, 249, 287, 295, 334, 335, 386, 391, 393, 395, 422, 478, 493, 497, 502, 519, 551, 583, 589, 614, 629, 634, 694, 697, 721, 731, 749, 755, 789, 802, 817, 843, 879, 898, 955, 958, 985, 989, 1003, 1037, 1079, 1114, 1154, 1159, 1177
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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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33 is a term because 33 = 3*11, 2*33 - 1 = 65 = 5*13 and 2*65 - 1 = 4*33 - 3 = 129 = 3*43.
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MATHEMATICA
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f[n_]:=Last/@FactorInteger[n]=={1, 1}; lst={}; Do[If[f[n]&&f[2*n-1]&&f[4*n-3], AppendTo[lst, n]], {n, 0, 7!}]; lst
tdpQ[n_]:=PrimeNu[n]==PrimeOmega[n]==PrimeNu[2n-1]==PrimeOmega[2n-1] == PrimeNu[4n-3]==PrimeOmega[4n-3]==2; Select[Range[1200], tdpQ] (* Harvey P. Dale, Nov 15 2020 *)
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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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