A231569 Composite numbers n such that lambda(n) divides 2n-2, where lambda is the Carmichael lambda function (A002322).

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

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 * A337812 A100390 A199768

Adjacent sequences: A231566 A231567 A231568 * A231570 A231571 A231572

Keyword

nonn

Author

José María Grau Ribas, Nov 11 2013

Status

approved