A353300 Numbers k such that A004394(k)-1 is prime.

3, 4, 5, 6, 8, 9, 11, 12, 13, 14, 15, 16, 19, 20, 24, 25, 26, 30, 32, 41, 47, 48, 49, 51, 57, 59, 76, 82, 83, 92, 104, 105, 117, 119, 131, 134, 137, 139, 143, 154, 166, 170, 172, 180, 209, 214, 215, 216, 217, 227, 231, 234, 247, 265, 269, 271, 284, 317, 327, 348

Offset: 1

Author

Amiram Eldar, Apr 10 2022

Keywords

• nonn

Comments

First differs from A306588 at n=15.

Examples

			3 is a term since A004394(3)-1 = 4-1 = 3 is prime.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..314

Crossrefs

Cf. A004394, A072826, A306588, A353301, A353302.

Programs

Mathematica

s = {}; abm = 0; k = 0; Do[ab = DivisorSigma[-1, n]; If[ab > abm, abm = ab; k++; If[PrimeQ[n - 1], AppendTo[s, k]]], {n, 1, 10^6}]; s