A077094 Starting the iteration of the function Phi[(Sigma[]-Phi[])] at these initial values leads to the fixed point 4.

4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 25, 26, 27, 28, 30, 32, 33, 34, 35, 38, 39, 44, 45, 46, 49, 51, 54, 55, 56, 57, 58, 62, 63, 65, 68, 70, 77, 85, 87, 91, 93, 95, 99, 104, 111, 119, 121, 129, 134, 143, 145, 153, 158, 161, 169, 189, 205, 209, 215, 221, 245

Offset

1,1

Comments

Probably this sequence is finite, with 92 terms of which the last is 6241.

Links

Table of n, a(n) for n=1..64.

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

Cf. A077090-A077100.

Sequence in context: A192506 A091212 A205783 * A210441 A343597 A199009

Adjacent sequences: A077091 A077092 A077093 * A077095 A077096 A077097

Keyword

nonn,fini

Author

Labos Elemer, Oct 31 2002

Extensions

Definition corrected by Harvey P. Dale, May 01 2021

Status

approved