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Search: id:A111206
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| A111206 |
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Semi-Sophie Germain semiprimes: semiprimes which are the product of Sophie Germain primes. |
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17
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| 4, 6, 9, 10, 15, 22, 25, 33, 46, 55, 58, 69, 82, 87, 106, 115, 121, 123, 145, 159, 166, 178, 205, 226, 249, 253, 262, 265, 267, 319, 339, 346, 358, 382, 393, 415, 445, 451, 466, 478, 502, 519, 529, 537, 562, 565, 573, 583, 586, 655, 667, 699, 717, 718, 753, 838
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Define an n-almost Sophie Germain almost-prime to be an n-almost prime all the prime factors of which are Sophie Germain primes. Note the contrast between this terminology and that of Sophie Germain n-almost primes, they are different.
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EXAMPLE
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a(4)=10 because 10 is the 4th semiprime both the prime factors of which are Sophie Germain primes.
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MATHEMATICA
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lst={}; Do[If[Plus@@Last/@FactorInteger[n]==2, a=First/@FactorInteger[n]; b=a[[1]]; k=0; If[Length[a]==2, c=a[[2]]; If[ !PrimeQ[2*c+1], k=1]]; If[PrimeQ[2*b+1]&&k==0, AppendTo[lst, n]]], {n, 7!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 27 2009]
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CROSSREFS
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Cf. A111153, A001358, A005384, A111207.
Sequence in context: A137167 A122492 A133234 this_sequence A087112 A077554 A118778
Adjacent sequences: A111203 A111204 A111205 this_sequence A111207 A111208 A111209
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KEYWORD
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nonn
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AUTHOR
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Christopher M. Tomaszewski (cmt1288(AT)comcast.net), Oct 24 2005
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Oct 31 2005
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