OFFSET
1,1
COMMENTS
See A158914 for the sequence for sigma_2.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..10000
MATHEMATICA
tp=DivisorSigma[1, Select[Range[1000], PrimeQ]]; tc=DivisorSigma[1, Select[Range[1000], !PrimeQ[ # ]&]]; Intersection[tp, tc]-1
PROG
(Sage) [sigma(n)-1 for n in (2..600) if is_prime(sigma(n)-1) and n<sigma(n)-1<600] # Giuseppe Coppoletta, Dec 22 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Mar 30 2009
STATUS
approved