A231570 Composite numbers n such that lambda(n) divides 3n-3, where lambda is the Carmichael lambda function (A002322).

9, 21, 45, 63, 65, 105, 117, 133, 231, 273, 341, 481, 561, 585, 645, 651, 1001, 1105, 1281, 1365, 1541, 1729, 2465, 2821, 3201, 3605, 4033, 4371, 4641, 4921, 5461, 5565, 6305, 6533, 6601, 7107, 7161, 8321, 8911, 10585, 11041, 12545, 13333, 13833, 14981

Offset: 1

Author

José María Grau Ribas, Nov 11 2013

Keywords

• nonn

Comments

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.

Crossrefs

Cf. A002322, A231569, A231571, A231572, A231573.

Programs

Mathematica

Select [1 + Range[100000], ! PrimeQ[#] && IntegerQ[3 (# -1)/ CarmichaelLambda[#]] &]

PARI

is(n)=!isprime(n) && (3*n-3)%lcm(znstar(n)[2])==0 && n>1 \\ Charles R Greathouse IV, Nov 13 2013