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A231571
Composite numbers n such that lambda(n) divides 4n-4, where lambda is the Carmichael lambda function (A002322).
3
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
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
KEYWORD
nonn
AUTHOR
STATUS
approved