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A230023
Numbers n such that sigma(phi(n)) = sigma(n) + phi(n).
3
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
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Oct 16 2013
STATUS
approved