Powerful digit sum

Problem 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, ab, where a, b < 100, what is the maximum digital sum?
def digitalsum(n):
    sum = 0
    for c in n:
        sum += int(c)
    return sum


def run(limit=100):
    maxsum = 0
    for a in range(1, limit):
        for b in range(1, limit):
            sum = digitalsum(str(a**b))
            if sum > maxsum:
                maxsum = sum
    return maxsum