A297361 Numbers k such that (3^lambda(k) - 1)/k is prime, where lambda(k) is the Carmichael lambda function (A002322).

4, 16, 40, 56, 160, 7280

Offset

1,1

Comments

The corresponding primes are 2, 5, 2, 13, 41, 73.

Links

Table of n, a(n) for n=1..6.

Example

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

Mathematica

aQ[n_] := PrimeQ[(3^CarmichaelLambda[n]-1)/n]; a={}; Do[If[aQ[k], AppendTo[a, k]], {k, 1, 10000}]; a

Prog

(PARI) isok(n) = (denominator(p=(3^lcm(znstar(n)[2])-1)/n)==1) && isprime(p); \\ Michel Marcus, Dec 29 2017

Crossrefs

Cf. A002322.

Sequence in context: A121318 A152133 A371345 * A210440 A329892 A220499

Adjacent sequences: A297358 A297359 A297360 * A297362 A297363 A297364

Keyword

nonn,more

Author

Amiram Eldar, Dec 29 2017

Status

approved