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A255510 Numbers n of the form 3^k such that sigma(n) is a prime p. 1

%I #28 Sep 08 2022 08:46:11

%S 9,729,531441,2503155504993241601315571986085849,

%T 4638397686588101979328150167890591454318967698009

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

%C Powers of 3 from A023194 (numbers n such that sigma(n) is a prime).

%H Jaroslav Krizek, <a href="/A255510/b255510.txt">Table of n, a(n) for n = 1..10</a>

%F a(n) = 3^(A028491(n) - 1).

%F sigma(a(n)) = A076481(n).

%t Select[3^Range[0,110],PrimeQ[DivisorSigma[1,#]]&] (* _Harvey P. Dale_, Mar 29 2015 *)

%o (Magma) [(3^n): n in [1..1000] | IsPrime((SumOfDivisors(3^n)))]

%Y Cf. A000203 (sigma), A023194 (sigma(n) is prime).

%Y Cf. A003462 (sigma(3^n)), A028491 (sigma(3^n) is prime) , A076481.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Mar 25 2015

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Last modified March 29 08:13 EDT 2024. Contains 371265 sequences. (Running on oeis4.)