OFFSET
1,1
COMMENTS
Contains all Mersenne primes (A000668) and squarefree products thereof (A046528 except 1). - Ivan Neretin, Feb 08 2017
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
EXAMPLE
sigma(57337)=2^16 hence 57337 is in the sequence.
MATHEMATICA
Select[Range[100000], PrimePowerQ[DivisorSigma[1, #]] &] (* Ivan Neretin, Feb 08 2017 *)
PROG
(PARI) for(n=1, 100000, if(omega(sigma(n)) == 1, print1(n, ", ")))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 14 2002
STATUS
approved