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