A255510 Numbers n of the form 3^k such that sigma(n) is a prime p.

9, 729, 531441, 2503155504993241601315571986085849, 4638397686588101979328150167890591454318967698009

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

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

Adjacent sequences: A255507 A255508 A255509 * A255511 A255512 A255513

Keyword

nonn

Author

Jaroslav Krizek, Mar 25 2015

Status

approved