Problem 3 Largest prime factor

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

import math

def is_prime(n):
if n < 2:return False
for i in range(2,int(math.sqrt(n))+1,1):
if not n % i :return False
return True

def run(n):
for i in range(3,int(math.sqrt(n))+1,2):
if not is_prime(i):continue
if n == i:return n
if not n % i: n = n / i

print run(13195)
print run(600851475143)