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A111351
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Semiprimes of the form 2*n + 1, where n is a square.
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3
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9, 33, 51, 129, 201, 289, 339, 393, 451, 579, 649, 723, 1059, 1569, 1923, 2049, 3043, 3873, 4609, 4803, 5001, 5619, 5833, 6051, 6499, 6729, 7201, 7939, 8193, 9249, 9523, 10083, 11553, 12169, 13123, 13449, 14113, 14451, 14793, 15843, 16201, 16563
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OFFSET
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1,1
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LINKS
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FORMULA
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MATHEMATICA
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Select[2Range[100]^2 + 1, Plus @@ Last /@ FactorInteger[ # ] == 2 &] (* Ray Chandler, Nov 10 2005 *)
Select[2*Range[100]^2+1, PrimeOmega[#]==2&] (* Harvey P. Dale, May 07 2013 *)
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PROG
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(Magma) IsSemiprime:=func<t | &+[d[2]: d in Factorization(t)] eq 2>; [s: t in [2..100] | IsSemiprime(s) where s is 2*t^2 + 1]; // Bruno Berselli, Sep 22 2012
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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