A098217 Cototients of terms from A098216. By definitions these cototient values are decimal repdigits.

0, 2, 4, 4, 3, 6, 8, 8, 7, 8, 9, 5, 9, 22, 11, 7, 44, 44, 66, 33, 88, 11, 33, 55, 88, 55, 99, 111, 77, 33, 99, 99, 111, 77, 77, 111, 55, 333, 55, 77, 444, 99, 333, 333, 77, 111, 77, 99, 77, 77, 777, 888, 888, 111, 99, 999, 777, 111, 99, 99, 555, 111, 999, 999, 999, 111, 1111

Offset: 1

Author

Labos Elemer, Oct 22 2004

Keywords

• nonn
• base

Comments

It is believed that for every repdigit r>1, inverse[cototient[r]] has solution, usually more than one.

Crossrefs

Cf. A096503, A010785, A098216.

Programs

Mathematica

ta={{0}};Do[s=Length[Union[IntegerDigits[n-EulerPhi[n]]]]; If[Equal[s, 1]&&!PrimeQ[n], Print[{n, n-EulerPhi[n]}];ta=Append[ta, n]], {n, 1, 100000}];ta=Delete[ta, 1];ta-EulerPhi[ta]