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A174653
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Semiprimes s such that neither s-1 nor s+1 is semiprime.
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1
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4, 6, 46, 49, 51, 55, 62, 65, 69, 74, 77, 82, 91, 106, 111, 115, 129, 155, 161, 166, 169, 183, 185, 187, 194, 209, 221, 226, 235, 237, 247, 249, 259, 262, 265, 267, 274, 278, 287, 289, 291, 295, 305, 309, 314, 319, 321, 323, 329, 339, 341, 346, 355, 358, 365
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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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EXAMPLE
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a(1)=4 because 4-1 = 3 (not semiprime) and 4+1 = 5 (not semiprime).
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MATHEMATICA
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Mean/@SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 400}], {0, 1, 0}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 19 2019 *)
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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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