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A161508
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Numbers n such that 2^n-1 has only one primitive prime factor.
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2
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2, 3, 4, 5, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 26, 27, 30, 31, 32, 33, 34, 38, 40, 42, 46, 49, 54, 56, 61, 62, 65, 69, 77, 78, 80, 85, 86, 89, 90, 93, 98, 107, 120, 122, 126, 127, 129, 133, 145, 147, 150, 158, 165, 170, 174, 184, 192, 195, 202, 208
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The corresponding prime p is in A161509. The binary expansion of 1/p has period n and this is the only prime with such a period. The binary analogue of A007498. This sequence has many terms in common with A072226, the n for which Phi(n,2) is prime. A072226 has the additional term 6; but it does not have terms 18, 20, 21, 54, 147, 342, 602, and 889 (less than 10000).
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..179
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FORMULA
| n such that A086251(n) = 1.
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MATHEMATICA
| Select[Range[1000], PrimePowerQ[Cyclotomic[ #, 2]/GCD[Cyclotomic[ #, 2], # ]]&]
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CROSSREFS
| Sequence in context: A114994 A137706 A039224 * A039264 A039161 A032797
Adjacent sequences: A161505 A161506 A161507 * A161509 A161510 A161511
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Jun 17 2009
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