A231571 Composite numbers n such that lambda(n) divides 4n-4, where lambda is the Carmichael lambda function (A002322).

4, 6, 8, 10, 12, 15, 16, 20, 24, 28, 30, 40, 48, 52, 60, 66, 70, 80, 85, 91, 112, 120, 130, 176, 190, 208, 232, 240, 276, 280, 286, 364, 370, 435, 451, 496, 520, 532, 561, 616, 703, 742, 910, 946, 976, 1036, 1105, 1128, 1288, 1387, 1456, 1729, 1770, 1891

Offset: 1

Author

José María Grau Ribas, Nov 11 2013

Keywords

• nonn

Comments

Contains the Carmichael numbers (A002997) and A231569.

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, A231570, A231572, A231573.

Programs

Mathematica

Select [1 + Range[100000], ! PrimeQ[#] && IntegerQ[4 (# -1)/ CarmichaelLambda[#]] &]

PARI

is(n)=!isprime(n) && (4*n-4)%lcm(znstar(n)[2])==0 && n>1 \\ Charles R Greathouse IV, Nov 13 2013