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A085724
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Numbers n such that 2^n - 1 is a semiprime (A001358).
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6
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4, 9, 11, 23, 37, 41, 49, 59, 67, 83, 97, 101, 103, 109, 131, 137, 139, 149, 167, 197, 199, 227, 241, 269, 271, 281, 293, 347, 373, 379, 421, 457, 487, 523, 727, 809, 881, 971, 983, 997
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| J. Earls, Mathematical Bliss, Pleroma Publications, 2009, pages 56-60. ASIN: B002ACVZ6O [From Jason Earls (zevi_35711(AT)yahoo.com), Nov 22 2009]
J. Earls, "Cole Semiprimes," Mathematical Bliss, Pleroma Publications, 2009, pages 56-60. ASIN: B002ACVZ6O [From Jason Earls (zevi_35711(AT)yahoo.com), Nov 25 2009]
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LINKS
| S. S. Wagstaff, Jr., The Cunningham Project
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EXAMPLE
| 11 is a member because 2^11-1=23*89
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MATHEMATICA
| SemiPrimeQ[n_]:=(n>1) && (2==Plus@@(Transpose[FactorInteger[n]][[2]])); Select[Range[100], SemiPrimeQ[2^#-1]&] (Noe)
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CROSSREFS
| Cf. A092558, A092559, A092561 and A092562.
Sequence in context: A141365 A179055 A002641 * A106854 A099458 A069219
Adjacent sequences: A085721 A085722 A085723 * A085725 A085726 A085727
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KEYWORD
| nonn,more
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Jul 20 2003
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EXTENSIONS
| More terms from Zak Seidov (zakseidov(AT)yahoo.com), Feb 27 2004
More terms from Cunningham project, Mar 23 2004
More terms from the Cunningham project sent by Robert G. Wilson v and T. D. Noe (noe(AT)sspectra.com), Feb 22 2006
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