HP 50g can't solve equation

[gor1060]

Function f(x)=sum(x^(s-1),s,1,x)-9 has discontinuity at a point x=3. From the left side of it function has value equal to -5 and from the right side it has value equal to 4.

           

No one CAS can't solve equation sum(x^(s-1),s,1,x)=9 because it's solution not exist.