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Search: id:A122498
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| 4, 9, 21, 49, 65, 86, 265, 1081, 1897, 2513, 7739, 97229, 128801, 299426
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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Eric Weisstein's World of Mathematics, "Semiprime." http://mathworld.wolfram.com/Semiprime.html
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FORMULA
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p(n)=p(n-2)+p(n-3)=A000931[n] a(n) = If [SemiprimeQ[p(n)==True,p(n)]
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MATHEMATICA
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SemiprimeQ[1] := False SemiprimeQ[n_Integer] := Plus @@ (Last /@ FactorInteger[n]) == 2 a = Table[ SeriesCoefficient[ Series[x/(1 - x^2 - x^3), {x, 0, 50}], n], {n, 0, 50}] f[n_] = If[SemiprimeQ[a[[n]]] == True, a[[n]], {}] Flatten[Table[f[n], {n, 1, Length[a]}]]
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CROSSREFS
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Cf. A000931, A053409.
Adjacent sequences: A122495 A122496 A122497 this_sequence A122499 A122500 A122501
Sequence in context: A027973 A103040 A084861 this_sequence A132750 A048582 A069231
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KEYWORD
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nonn,uned
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AUTHOR
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Roger Bagula (rlbagulatftn(AT)yahoo.com), Sep 15 2006
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