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4, 9, 15, 21, 33, 38, 58, 86, 106, 122, 485, 905, 1939, 4163, 6697, 12381, 14473, 22889, 107833, 170769, 370729, 687634, 804106, 1093762, 1276259, 2767999, 11140379, 15186449, 210634829, 286937249, 391048473, 532793518, 725995178, 847539571
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listen;
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internal format)
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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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276799 is an element of this sequence because A103372(99) = 276799 and 276799 is semiprime because 276799 = 31 * 8929 where both 31 and 8929 are primes.
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MATHEMATICA
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SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 4; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 150], SemiprimeQ]]
Union[Select[LinearRecurrence[{0, 0, 0, 1, 1}, {1, 1, 1, 1, 1}, 150], PrimeOmega[#] == 2&]] (* Harvey P. Dale, Apr 22 2015 *)
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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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