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A163162 Numbers n such that sigma(n) is not prime. 2
1, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

FORMULA

A000027 \ A023194.

a(n) ~ n. - Charles R Greathouse IV, May 27, 2011

EXAMPLE

a(1)=1 because A000203(1) is not prime. a(2)=3 because A000203(3)=3 is not prime. a(3)=5 because sigma(5)=6 is not prime.

MATHEMATICA

Select[Range[1000], ! PrimeQ[DivisorSigma[1, #]]&] (* Vincenzo Librandi, Jan 18 2013 *)

PROG

(MAGMA)[n: n in [1..80]| not IsPrime(SumOfDivisors(n))];  // Vincenzo Librandi, Jan 18 2013

CROSSREFS

Complement of A023194.

Cf. A000203.

Sequence in context: A254130 A114978 A138891 * A181744 A160685 A080218

Adjacent sequences:  A163159 A163160 A163161 * A163163 A163164 A163165

KEYWORD

nonn,easy

AUTHOR

Juri-Stepan Gerasimov, Jul 22 2009

EXTENSIONS

Edited by R. J. Mathar, Jul 25 2009

STATUS

approved

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Last modified August 18 15:00 EDT 2019. Contains 326106 sequences. (Running on oeis4.)