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Search: id:A104876
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| A104876 |
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Semiprimes of the form primorial(n) - 1. |
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+0
2
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| 209, 510509, 6469693229, 200560490129, 13082761331670029, 1922760350154212639069, 557940830126698960967415389, 40729680599249024150621323469, 2305567963945518424753102147331756069
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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S. M. Ruiz, "A Result on Prime Numbers." Math. Gaz. 81, 269, 1997.
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LINKS
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Eric Weisstein's World of Mathematics, Primorial.
Eric Weisstein's World of Mathematics, Semiprime.
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FORMULA
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n# - 1 iff semiprime. Equals {A002110(i) - 1} intersection {A001358(j)}.
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EXAMPLE
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4# - 1 = 209 = 11 * 19.
7# - 1 = 510509 = 61 * 8369.
10# - 1 = 6469693229 = 79 * 81894851.
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MATHEMATICA
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From Ray Chandler: Bigomega[n_]:=Plus@@Last/@FactorInteger[n]; SemiprimeQ[n_]:=Bigomega[n]?2; Primorial[n_]:=Product[Prime[i], {i, n}]; Select[Table[Primorial[n]-1, {n, 30}], SemiprimeQ]
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CROSSREFS
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Cf. A001358, A002110, A034386, A005234, A014545, A018239, A006794, A057704, A057705, A104877.
Sequence in context: A003779 A071379 A125549 this_sequence A050516 A100670 A025392
Adjacent sequences: A104873 A104874 A104875 this_sequence A104877 A104878 A104879
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 28 2005
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EXTENSIONS
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Entry revised by N. J. A. Sloane (njas(AT)research.att.com), Apr 01 2006
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