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A122498
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A000931 Padovan numbers that are semiprimes.
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0
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4, 9, 21, 49, 65, 86, 265, 1081, 1897, 2513, 7739, 97229, 128801, 299426
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| Eric Weisstein's World of Mathematics, "Semiprime." http://mathworld.wolfram.com/Semiprime.html
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FORMULA
| p(n)=p(n-2)+p(n-3)=A000931[n] a(n) = If [SemiprimeQ[p(n)==True,p(n)]
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MATHEMATICA
| 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
| Cf. A000931, A053409.
Sequence in context: A027973 A103040 A084861 * A132750 A048582 A069231
Adjacent sequences: A122495 A122496 A122497 * A122499 A122500 A122501
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KEYWORD
| nonn,uned
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AUTHOR
| Roger Bagula (rlbagulatftn(AT)yahoo.com), Sep 15 2006
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