A367460 Numbers k such that 3^sigma(k) - k is a prime.

1, 10, 52, 400, 2480, 7202, 28222

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