login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 18 04:48 EST 2020. Contains 332011 sequences. (Running on oeis4.)