A230023 Numbers n such that sigma(phi(n)) = sigma(n) + phi(n).

3597, 3955, 5635, 1388763, 3155577, 6718173, 10541751, 11333043, 12331467, 15477033, 18454809, 19062465, 21229131, 25243618, 32750823, 38975607, 41126645, 42756555, 45016767, 48072753, 73061703, 81409317, 84235965, 87999021, 93936513, 106749513, 128812167

Offset

1,1

Links

Donovan Johnson, Table of n, a(n) for n = 1..187 (terms < 3*10^10)

Example

phi(3597)=2160, sigma(3597)=5280, sigma(2160)=7440 so sigma(phi(3597))=7440=5280+2160=sigma(3597)+phi(3597) and 3597 is in the sequence.

Mathematica

Do[If[DivisorSigma[1, EulerPhi[n]] == DivisorSigma[1, n] + EulerPhi[n], Print[n]], {n, 200000000}]
spQ[n_]:=Module[{phi=EulerPhi[n]}, DivisorSigma[1, phi]==DivisorSigma[ 1, n]+ phi]; Select[Range[129*10^6], spQ] (* Harvey P. Dale, Aug 06 2020 *)

Crossrefs

Cf. A000010, A000203, A062402.

Sequence in context: A187422 A186214 A188100 * A157857 A141781 A348627

Adjacent sequences: A230020 A230021 A230022 * A230024 A230025 A230026

Keyword

nonn

Author

Farideh Firoozbakht, Oct 16 2013

Status

approved