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A305755
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Odd semiprimes sandwiched by even semiprimes.
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0
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9, 25, 33, 35, 39, 77, 85, 95, 141, 155, 201, 259, 355, 361, 395, 481, 559, 565, 623, 763, 799, 841, 865, 879, 923, 933, 979, 1003, 1043, 1177, 1199, 1219, 1227, 1285, 1293, 1299, 1437, 1441, 1517, 1541, 1603, 1643, 1655, 1717, 1769, 1865, 2005, 2041, 2095, 2101, 2123, 2127, 2183, 2245
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OFFSET
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1,1
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COMMENTS
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Odd semiprimes sp(k) = A001358(k) such that sp(k-1) and sp(k+1) are even. Values of k: 3, 9, 11, 13, 15, 26, 28, 34, 46, 51, 63, 83, 112, 114, 125, 148, 175, 177, 190, 230, 242, 253, 259, 264, 278, 280, 293.
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LINKS
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EXAMPLE
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MATHEMATICA
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s = Select[Range[2300], Plus @@ Last /@ FactorInteger[#] == 2 &]; Transpose[ Select[ Partition[s, 3, 1], Mod[#, 2] == {0, 1, 0} &]][[2]] (* Giovanni Resta, Jun 10 2018 *)
Module[{nn=2500, sp}, sp=Select[Range[nn], PrimeOmega[#]==2&]; Select[Partition[ sp, 3, 1], Mod[ #, 2] =={0, 1, 0}&]][[;; , 2]] (* Harvey P. Dale, Mar 03 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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