Problem 63 - How many n-digit positive integers exist which are also an nth power?

링크

The 5-digit number, 16807=7⁵, is also a fifth power. Similarly, the 9-digit number, 134217728=8⁹, is a ninth power.

How many n-digit positive integers exist which are also an nth power?

python

sum(len(str(a**b)) == b for a in range(1, 10) for b in range(1, 22))