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A050384 Nonprimes such that n and phi(n) are relatively prime. 8
1, 15, 33, 35, 51, 65, 69, 77, 85, 87, 91, 95, 115, 119, 123, 133, 141, 143, 145, 159, 161, 177, 185, 187, 209, 213, 215, 217, 221, 235, 247, 249, 255, 259, 265, 267, 287, 295, 299, 303, 319, 321, 323, 329, 335, 339, 341, 345, 365, 371, 377, 391, 393, 395, 403 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also nonprimes n such that there is only one group of order n, i.e., A000001(n) = 1.

Intersection of A018252 and A003277.

Also numbers n such that n and A051953(n) are relatively prime. - Labos Elemer

Apart from the first term, this is a subsequence of A024556. - Charles R Greathouse IV, Apr 15 2015

Every Carmichael number and each of its nonprime divisors is in this sequence. - Emmanuel Vantieghem, Apr 20 2015

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[450], !PrimeQ[#] && GCD[#, EulerPhi[#]] == 1&] (* Harvey P. Dale, Jan 31 2011 *)

PROG

(PARI) is(n)=!isprime(n) && gcd(eulerphi(n), n)==1 \\ Charles R Greathouse IV, Apr 15 2015

CROSSREFS

If the primes are included we get A003277. Cf. A000001, A000010 (phi).

Sequence in context: A154369 A243592 A089966 * A142862 A053343 A068081

Adjacent sequences:  A050381 A050382 A050383 * A050385 A050386 A050387

KEYWORD

nonn

AUTHOR

Christian G. Bower, Nov 15 1999

STATUS

approved

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Last modified August 19 14:06 EDT 2017. Contains 290808 sequences.