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

1,1

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.

Mathematica

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

Prog

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

Crossrefs

Cf. A002322, A231569, A231570, A231572, A231573.

Sequence in context: A289425 A225514 A161546 * A286043 A310658 A167179

Adjacent sequences: A231568 A231569 A231570 * A231572 A231573 A231574

Keyword

nonn

Author

José María Grau Ribas, Nov 11 2013

Status

approved