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A255510
Numbers n of the form 3^k such that sigma(n) is a prime p.
1
9, 729, 531441, 2503155504993241601315571986085849, 4638397686588101979328150167890591454318967698009
OFFSET
1,1
COMMENTS
Powers of 3 from A023194 (numbers n such that sigma(n) is a prime).
LINKS
FORMULA
a(n) = 3^(A028491(n) - 1).
sigma(a(n)) = A076481(n).
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
Cf. A000203 (sigma), A023194 (sigma(n) is prime).
Cf. A003462 (sigma(3^n)), A028491 (sigma(3^n) is prime) , A076481.
Sequence in context: A053847 A053854 A053764 * A122251 A234611 A015481
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Mar 25 2015
STATUS
approved