Euler Project 56

A googol (10¹⁰⁰) is a massive number: one followed by one-hundred zeros; 100¹⁰⁰ is almost unimaginably large: one followed by two-hundred zeros. Despite their size, the sum of the digits in each number is only 1.
Considering natural numbers of the form, a^b, where a, b 100, what is the maximum digital sum?
My Solution
(defun DigitalSum(n)

(let* ((numberstr (format nil "~a" n)))

(loop for i from 0 to (- (length numberstr) 1)

sum (parse-integer numberstr :start i :end (+ i 1)))))

(defun Euler56()

(loop for i from 2 to 99

do(loop for j from 2 to 99

do(print (DigitalSum (expt i j))))))