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A231570 Composite numbers n such that lambda(n) divides 3n-3, where lambda is the Carmichael lambda function (A002322). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..45.

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A231569-A231575, A002322.

Sequence in context: A163205 A154862 A020137 * A020190 A225507 A135187

Adjacent sequences:  A231567 A231568 A231569 * A231571 A231572 A231573

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Nov 11 2013

STATUS

approved

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Last modified June 19 05:26 EDT 2019. Contains 324218 sequences. (Running on oeis4.)