OFFSET
1,2
COMMENTS
a(8) > 67569.
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
KEYWORD
nonn,more
AUTHOR
J.W.L. (Jan) Eerland, Jan 26 2024
EXTENSIONS
a(7) from Michael S. Branicky, Jan 27 2024
STATUS
approved