OFFSET
1,1
COMMENTS
Powers of 3 from A023194 (numbers n such that sigma(n) is a prime).
LINKS
Jaroslav Krizek, Table of n, a(n) for n = 1..10
MATHEMATICA
Select[3^Range[0, 110], PrimeQ[DivisorSigma[1, #]]&] (* Harvey P. Dale, Mar 29 2015 *)
PROG
(Magma) [(3^n): n in [1..1000] | IsPrime((SumOfDivisors(3^n)))]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Mar 25 2015
STATUS
approved