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A231569 Composite numbers n such that lambda(n) divides 2n-2, where lambda is the Carmichael lambda function (A002322). 6
4, 6, 8, 12, 15, 24, 28, 66, 91, 276, 435, 532, 561, 616, 703, 946, 1105, 1128, 1288, 1729, 1891, 2465, 2701, 2821, 2926, 3367, 5551, 6601, 8646, 8695, 8911, 10585, 11305, 11476, 12403, 13981, 15051, 15841, 16471, 18721, 19096, 23001, 26335, 29341, 30889 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Contains the Carmichael numbers (A002997).

Conjecture: the relative asymptotic density of the Carmichael numbers in this sequence exists, is positive and smaller than 1.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

J. M. Grau and Antonio Oller-Marcén, Generalizing Giuga's conjecture, arXiv:1103.3483 [math.NT], 2011.

MATHEMATICA

Select [1 + Range[100000], ! PrimeQ[#] && IntegerQ[2 (# -1)/ CarmichaelLambda[#]] &]

PROG

(PARI) is(n)=!isprime(n) && (2*n-2)%lcm(znstar(n)[2])==0 && n>1 \\ Charles R Greathouse IV, Nov 13 2013

CROSSREFS

Cf. A002322, A002997, A231570, A231571, A231572, A231573.

Sequence in context: A239439 A325601 A310662 * A100390 A199768 A157932

Adjacent sequences:  A231566 A231567 A231568 * A231570 A231571 A231572

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Nov 11 2013

STATUS

approved

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Last modified April 4 19:22 EDT 2020. Contains 333229 sequences. (Running on oeis4.)