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A367460
Numbers k such that 3^sigma(k) - k is a prime.
0
1, 10, 52, 400, 2480, 7202, 28222
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)]
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
a(7) from Michael S. Branicky, Jan 27 2024
STATUS
approved