If x is composite then we know:
c*x/log(log(x))<phi(x)<=xsqrt(x), where c>0 is a constant [c=0.25 is good for all x>6].
ok, not very elegant to use these, though this is still elementary.
With this you can easily solve the problem, the remaining x=m^n+n prime case is very easy.
Last fiddled with by R. Gerbicz on 20210213 at 21:47
