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A297362 Numbers n such that (2^ord(2, n) - 1)/n is prime, where ord(2, n) is the multiplicative order of 2 (mod n). 0
5, 9, 21, 23, 33, 47, 51, 73, 85, 89, 93, 129, 167, 217, 223, 263, 315, 341, 381, 585, 819, 1057, 1365, 3591, 3855, 4681, 4871, 5461, 6141, 6223, 6719, 7487, 8193, 11447, 13107, 13367, 13797, 14329, 16513, 18631, 21845, 24573, 25575, 26431, 33825, 37449 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The corresponding primes are 3, 7, 3, 89, 31, 178481, 5, 7, 3, 23, 11, ...

LINKS

Table of n, a(n) for n=1..46.

EXAMPLE

5 is in the sequence since ord(2, 5) = 4 and (2^4 - 1)/5 = 3 is prime.

MATHEMATICA

aQ[n_] := PrimeQ[(2^MultiplicativeOrder[2, n] - 1)/n]; Select[Range[10000], aQ]

CROSSREFS

Cf. A002326, A165781.

Sequence in context: A273150 A273388 A273449 * A175364 A244642 A211424

Adjacent sequences:  A297359 A297360 A297361 * A297363 A297364 A297365

KEYWORD

nonn

AUTHOR

Amiram Eldar, Dec 29 2017

STATUS

approved

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Last modified April 22 07:26 EDT 2021. Contains 343163 sequences. (Running on oeis4.)