OFFSET
1,1
COMMENTS
The only prime for which this equation has a solution is 3.
MATHEMATICA
a[n_] := Select[Range[n-1], EulerPhi[n]==EulerPhi[n-# ]+EulerPhi[ # ]&]; t=Table[Length[a[n]], {n, 1000}]; Complement[Flatten[Position[t, 0]], Prime[Range[PrimePi[1000]]]]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Jul 15 2005
STATUS
approved