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A078893 Composite numbers n such that phi(n) - 1 is prime, where phi is Euler's totient function (A000010). 2
8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 24, 25, 26, 27, 28, 30, 33, 35, 36, 38, 39, 42, 44, 45, 49, 50, 51, 52, 54, 56, 62, 64, 65, 66, 68, 69, 70, 72, 77, 78, 80, 81, 84, 86, 90, 91, 92, 93, 95, 96, 98, 99, 102, 104, 105, 111, 112, 117, 120, 121, 122, 123, 124, 129, 130, 133 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A078892 with the primes removed. - Ray Chandler, May 26 2008

LINKS

Table of n, a(n) for n=1..66.

PROG

(PARI) is(n)=!isprime(n) && isprime(eulerphi(n)-1) \\ Charles R Greathouse IV, Feb 21 2013

CROSSREFS

Cf. A000010, A000040, A008864, A109606, A078892, A066071, A068019.

Sequence in context: A097363 A152870 A181723 * A050704 A024884 A031009

Adjacent sequences:  A078890 A078891 A078892 * A078894 A078895 A078896

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 12 2002

STATUS

approved

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Last modified September 17 09:11 EDT 2019. Contains 327128 sequences. (Running on oeis4.)