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A247071 Numbers n such that 2^n-1 has only one primitive prime factor, sorted according to the magnitude of the corresponding prime. 0
2, 4, 3, 10, 12, 8, 18, 5, 20, 14, 9, 7, 15, 24, 16, 30, 21, 22, 26, 42, 13, 34, 40, 32, 54, 17, 38, 27, 19, 33, 46, 56, 90, 78, 62, 31, 80, 120, 126, 150, 86, 98, 49, 69, 65, 174, 77, 93, 122, 61, 85, 192, 170, 234, 158, 165, 147, 129, 184, 89, 208, 312 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Periods associated with A144755 in base 2. The binary analog of A051627.

LINKS

Table of n, a(n) for n=1..62.

EXAMPLE

2^12 - 1 = 4095 = 3 * 3 * 5 * 7 * 13, but none of 3, 5, 7 is a primitive prime factor, so the only primitive prime factor of 2^12 - 1 is 13.

MATHEMATICA

nmax = 65536; primesPeriods = Reap[Do[p = Cyclotomic[n, 2]/GCD[n, Cyclotomic[n, 2]]; If[PrimeQ[p], Print[n]; Sow[{p, n}]], {n, 1, nmax}]][[2, 1]]; Sort[primesPeriods][[All, 2]]

CROSSREFS

Cf. A161508, A161509, A144755, A007498, A007615, A051627, A040017.

Sequence in context: A208324 A277416 A064691 * A014664 A270600 A180871

Adjacent sequences:  A247068 A247069 A247070 * A247072 A247073 A247074

KEYWORD

nonn

AUTHOR

Eric Chen, Nov 16 2014

STATUS

approved

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Last modified August 26 05:20 EDT 2019. Contains 326328 sequences. (Running on oeis4.)