OFFSET
1,1
COMMENTS
Probably this sequence is finite, with 92 terms of which the last is 6241.
EXAMPLE
n=6241: FixedPointList={6241,104,54,32,20,16,22,12,8,10,6,4},end=4.
MATHEMATICA
f[x_] := EulerPhi[DivisorSigma[1, x]-EulerPhi[x]] Do[s=NestList[f, n, 100]; s1=Part[s, 99]; s2=Part[s, 100]; If[Equal[s1, s2]&&Equal[s1, 4], Print[{n, s1}]], {n, 1, 1000000}]
f4[n_]:=FixedPoint[EulerPhi[DivisorSigma[1, #]-EulerPhi[#]]&, n, 50]==4; Select[Range[250], f4] (* Harvey P. Dale, May 01 2021 *)
CROSSREFS
KEYWORD
nonn,fini
AUTHOR
Labos Elemer, Oct 31 2002
EXTENSIONS
Definition corrected by Harvey P. Dale, May 01 2021
STATUS
approved