A377927 Numbers k such that 4^sigma(k) - k is a prime.

1, 5, 17, 57, 675, 1329, 1425, 3803, 39617

Offset: 1

Author

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

Keywords

• nonn
• more

Examples

			17 is in the sequence because 4^sigma(17) - 17 = 4^18 - 17 = 68719476719 is prime.
		

Crossrefs

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

Programs

Magma

[n: n in[1..10000] | IsPrime((4^SumOfDivisors(n)) - n)];

Mathematica

a[n_] := Select[Range@ n, PrimeQ[4^DivisorSigma[1, #] - #] &]; a[20000]
DeleteCases[ParallelTable[If[PrimeQ[4^DivisorSigma[1,k]-k],k,n],{k,1,10^4}],n]

Extensions

a(9) from Michael S. Branicky, Nov 11 2024