A098217 - OEIS

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

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OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..67.

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]

CROSSREFS

Cf. A096503, A010785, A098216.

Sequence in context: A079533 A072872 A135359 * A151846 A131118 A140765

Adjacent sequences: A098214 A098215 A098216 * A098218 A098219 A098220

KEYWORD

nonn,base

AUTHOR

Labos Elemer, Oct 22 2004

STATUS

approved