OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) ~ n. - Charles R Greathouse IV, May 27 2011
EXAMPLE
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
(PARI) isok(k) = !isprime(sigma(k)); \\ Michel Marcus, Mar 10 2022
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Jul 22 2009
EXTENSIONS
Edited by R. J. Mathar, Jul 25 2009
STATUS
approved