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A297360 Numbers k such that (2^lambda(k) - 1)/k is prime, where lambda(k) is the Carmichael lambda function (A002322). 0
5, 9, 21, 33, 255, 315, 585, 819, 1365, 3591 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The corresponding primes are 3, 7, 3, 31, 257, 13, 7, 5, 3, 73, ...

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

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

MATHEMATICA

aQ[n_] := PrimeQ[(2^CarmichaelLambda[n]-1)/n]; a={}; Do[If[aQ[k], AppendTo[a, k]], {k, 1, 4000, 2}]; a

PROG

(PARI) isok(n) = (denominator(p=(2^lcm(znstar(n)[2])-1)/n)==1) && isprime(p); \\ Michel Marcus, Dec 29 2017

CROSSREFS

Cf. A002322.

Sequence in context: A146867 A068481 A146827 * A216414 A147018 A081883

Adjacent sequences:  A297357 A297358 A297359 * A297361 A297362 A297363

KEYWORD

nonn,more

AUTHOR

Amiram Eldar, Dec 29 2017

STATUS

approved

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Last modified May 18 19:51 EDT 2022. Contains 353824 sequences. (Running on oeis4.)