A090999 Numbers k such that sigma(k)-k = pi(sigma(k)).

1, 15, 21, 33, 23069, 42029, 148031, 209911, 3271099

Offset: 1

Author

Naohiro Nomoto, Mar 01 2004

Keywords

• nonn
• more

Crossrefs

Cf. A000203 (sigma), A000720 (pi), A001065, A070803.

Programs

Mathematica

Do[If[DivisorSigma[1, n]-n==PrimePi[DivisorSigma[1, n]], Print[n]], {n, 1, 10000}]

PARI

isok(k) = {my(s = sigma(k)); s - k == primepi(s);} \\ Amiram Eldar, Jun 20 2025

Extensions

a(9) from Amiram Eldar, Jun 20 2025