OFFSET
1,2
COMMENTS
Obviously only for n = 1, prime(n) = 2*sigma(n).
It is interesting that all terms of the sequence A112587 are in the sequence and this sequence has only two more terms 96 & 180. Hence if phi(n) <= 2*tau(n) then prime(n) <= 2*sigma(n).
MATHEMATICA
Select[Range[200], Prime[#] <= 2DivisorSigma[1, #]&]
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Farideh Firoozbakht, Oct 17 2014
STATUS
approved