Each of the capital letters in bold denotes a different base ten digit from 1 to 9 in this cryptarithmetic expression:
A^{B/C} + D^{E/F} + G^{H/I}
(I) Determine the respective smallest and the largest positive integer that this expression can assume.
(II) Determine the respective smallest and the largest prime number that this expression can assume. What are the respective smallest and the largest palindrome assumed by the above expression?