OFFSET
1,2
COMMENTS
When iteration of f[]=Phi[Sigma[]-Phi[]] is started at various initial values, not ending in cycles and converging, it ends at these fixed points.
a(28) <= 11435212800. a(29) <= 15083274240. a(30) <= 90215424000. [From Donovan Johnson, Dec 14 2009]
EXAMPLE
n=30: FixedPointList={30,32,46,20,16,22,12,8,10,6,4},end=4; n=94: FixedPointList={94,42,24},end=24. n=41708: FixedPointList={41708,26064,32352,21216,15232,8064},end=8064; n=12100: FixedPointList={12100,24000,34944},end=34944.
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]&&!PrimeQ[n], Print[{n, s1}]], {n, 1, 1000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 31 2002
EXTENSIONS
a(9) corrected and a(11)-a(27) from Donovan Johnson, Dec 14 2009
STATUS
approved