1,2

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

A000027 \ A023194.

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

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.

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

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

Complement of A023194.

Cf. A000203.

Sequence in context: A254130 A114978 A138891 * A181744 A160685 A080218

Adjacent sequences: A163159 A163160 A163161 * A163163 A163164 A163165

nonn,easy

Juri-Stepan Gerasimov, Jul 22 2009

Edited by R. J. Mathar, Jul 25 2009

approved