This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A255510 #28 Sep 08 2022 08:46:11 %S A255510 9,729,531441,2503155504993241601315571986085849, %T A255510 4638397686588101979328150167890591454318967698009 %N A255510 Numbers n of the form 3^k such that sigma(n) is a prime p. %C A255510 Powers of 3 from A023194 (numbers n such that sigma(n) is a prime). %H A255510 Jaroslav Krizek, <a href="/A255510/b255510.txt">Table of n, a(n) for n = 1..10</a> %F A255510 a(n) = 3^(A028491(n) - 1). %F A255510 sigma(a(n)) = A076481(n). %t A255510 Select[3^Range[0,110],PrimeQ[DivisorSigma[1,#]]&] (* _Harvey P. Dale_, Mar 29 2015 *) %o A255510 (Magma) [(3^n): n in [1..1000] | IsPrime((SumOfDivisors(3^n)))] %Y A255510 Cf. A000203 (sigma), A023194 (sigma(n) is prime). %Y A255510 Cf. A003462 (sigma(3^n)), A028491 (sigma(3^n) is prime) , A076481. %K A255510 nonn %O A255510 1,1 %A A255510 _Jaroslav Krizek_, Mar 25 2015