A033872 Numbers k such that A033831(k) is prime.

8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 26, 27, 28, 30, 32, 33, 34, 35, 38, 39, 42, 44, 45, 46, 48, 50, 51, 52, 55, 56, 57, 58, 62, 63, 64, 65, 68, 69, 72, 74, 75, 76, 77, 80, 81, 82, 85, 86, 87, 90, 91, 92, 93, 94, 95, 98, 99

Offset: 1

Author

Naohiro Nomoto

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A033831.

Programs

Mathematica

f[n_] := DivisorSum[n, 1&, # > 2 && n/# < #-1 &]; Select[Range[1000], PrimeQ[f[#]] &] (* Amiram Eldar, Jun 11 2019 *)

PARI

isok(n) = isprime(sumdiv(n, d, (d>=3) && (q=n/d) && (q>=1) && (q<=d-2))); \\ Michel Marcus, Jun 11 2019