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 A367460 Numbers k such that 3^sigma(k) - k is a prime. 0
 1, 10, 52, 400, 2480, 7202, 28222 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(8) > 67569. LINKS Table of n, a(n) for n=1..7. EXAMPLE 10 is in the sequence because 3^sigma(10) - 10 = 3^18 - 10 = 387420479 is prime. MATHEMATICA a[n_] := Select[Range@ n, PrimeQ[3^DivisorSigma[1, #] - #] &]; a[20000] DeleteCases[ParallelTable[If[PrimeQ[3^DivisorSigma[1, k]-k], k, n], {k, 1, 10^4}], n] PROG (Magma) [n: n in[1..10000] | IsPrime((3^SumOfDivisors(n)) - n)] CROSSREFS Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851, A368651. Sequence in context: A092966 A281401 A050494 * A200035 A119543 A302302 Adjacent sequences: A367457 A367458 A367459 * A367461 A367462 A367463 KEYWORD nonn,more AUTHOR J.W.L. (Jan) Eerland, Jan 26 2024 EXTENSIONS a(7) from Michael S. Branicky, Jan 27 2024 STATUS approved

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Last modified August 10 22:34 EDT 2024. Contains 375058 sequences. (Running on oeis4.)