A377786 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A377786

Numbers k such that 5^sigma(k) - k is a prime.

0

4, 524, 7206, 11156

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

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

4 is in the sequence because 5^sigma(4) - 4 = 5^7 - 4 = 78121 is prime.

MATHEMATICA

a[n_] := Select[Range@ n, PrimeQ[5^DivisorSigma[1, #] - #] &]; a[20000]

DeleteCases[ParallelTable[If[PrimeQ[5^DivisorSigma[1, k]-k], k, n], {k, 1, 10^4}], n]

PROG

(Magma) [n: n in[1..10000] | IsPrime((5^SumOfDivisors(n)) - n)];

CROSSREFS

Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851, A368651, A367460, A377927.

Sequence in context: A003393 A089668 A257922 * A083284 A350613 A152218

Adjacent sequences: A377783 A377784 A377785 * A377787 A377788 A377789

KEYWORD

nonn,more

AUTHOR

J.W.L. (Jan) Eerland, Nov 11 2024

EXTENSIONS

a(4) from Michael S. Branicky, Nov 11 2024

STATUS

approved