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A161508 Numbers n such that 2^n-1 has only one primitive prime factor. 6
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; text; internal format)
OFFSET

1,1

COMMENTS

Also, numbers n such that A086251(n) = 1.

Also, numbers n such that A064078(n) is a prime power.

The corresponding primitive primes are listed in A161509.

The binary expansion of 1/p has period n and this is the only prime with such a period. The binary analog of A007498.

This sequence has many terms in common with A072226. A072226 has the additional term 6; but it does not have terms 18, 20, 21, 54, 147, 342, 602, and 889 (less than 10000).

LINKS

T. D. Noe, Table of n, a(n) for n=1..179

MATHEMATICA

Select[Range[1000], PrimePowerQ[Cyclotomic[ #, 2]/GCD[Cyclotomic[ #, 2], # ]]&]

PROG

(PARI) is_A161508(n) = my(t=polcyclo(n, 2)); isprimepower(t/gcd(t, n)); \\ Charles R Greathouse IV, Nov 17 2014

CROSSREFS

Sequence in context: A137706 A324766 A039224 * A039264 A231004 A039161

Adjacent sequences:  A161505 A161506 A161507 * A161509 A161510 A161511

KEYWORD

nonn

AUTHOR

T. D. Noe, Jun 17 2009

STATUS

approved

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Last modified August 20 05:25 EDT 2019. Contains 326139 sequences. (Running on oeis4.)