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Search: id:A109289
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| A109289 |
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Composite numbers which are not of the form p*q + 1, where p and q are distinct primes. |
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+0
4
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| 4, 6, 8, 9, 10, 12, 14, 18, 20, 21, 24, 25, 26, 28, 30, 32, 33, 38, 42, 44, 45, 46, 48, 49, 50, 51, 54, 55, 57, 60, 62, 64, 65, 68, 69, 72, 74, 76, 77, 80, 81, 82, 84, 85, 90, 91, 93, 98, 99, 100, 102, 104, 105, 106, 108, 110, 111, 114, 115, 117, 118, 121, 122, 125, 126, 128
(list; graph; listen)
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OFFSET
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1,1
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MATHEMATICA
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Select[Range[2, 130], ! (PrimeQ[ # ] || (Plus @@ Last /@ FactorInteger[ # - 1] == 2 && Length[FactorInteger[ # - 1]] == 2)) &] (*Chandler*)
fQ[n_] := Last /@ FactorInteger[n] != {1, 1}; Select[ Range[2, 128], !PrimeQ[ # ] && fQ[ # - 1] &] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A109287, A109288, A109290.
Sequence in context: A090419 A070810 A129930 this_sequence A066071 A067013 A071070
Adjacent sequences: A109286 A109287 A109288 this_sequence A109290 A109291 A109292
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KEYWORD
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easy,nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Aug 20 2005
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EXTENSIONS
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Extended by Robert G. Wilson v (rgwv(AT)rgwv.com) and Ray Chandler (rayjchandler(AT)sbcglobal.net), Aug 25 2005
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