A098218 Nonprime numbers whose cototient is a decimal repunits >1 from A002275.
35, 121, 231, 327, 535, 1111, 2047, 2407, 2911, 3127, 3327, 20767, 45967, 64111, 75847, 81607, 103927, 177367, 202207, 210767, 224295, 234607, 275647, 277807, 290911, 295447, 305887, 308911, 321407, 333327, 453911, 475967, 586127, 1199327
Offset: 1
Examples
n=1111 and cototient(1111)=111. By accident, both n and its cototient are decimal repunits.
Links
- Donovan Johnson, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
ta={{0}};Do[s=Length[u=Union[IntegerDigits[n-EulerPhi[n]]]]; If[Equal[s, 1]&&!PrimeQ[n]&&Equal[u, {1}], Print[{n, n-EulerPhi[n]}]; ta=Append[ta, n]], {n, 1, 100000}];ta=Delete[ta, 1];ta-EulerPhi[ta]
Comments