Can't escape from sign question loop



Define

  ss(a,N):=(print([a,N,i]),sum(i^a,i,0,N));

Now do

  plot2d(ss(.5,i),[i,0,5]);

Maxima repeatedly asks the sign of i, and control-G cannot escape from
this.  I do understand that when N is a non-integer, the sum will
return a noun form.  But that should be OK.

Two problems:

1) It asking the sign of i?
2) I escape from this infinite loop using control-G?

Thoughts?

            -s