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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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 14 10:47 EDT 2020. Contains 336480 sequences. (Running on oeis4.)