第三解:

The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ?

解:

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feed = 600851475143
def GetFactor(feed,footmark):
while footmark < feed:
footmark += 2
if feed % footmark == 0:
print footmark
GetFactor(feed / footmark,footmark)
break
GetFactor(feed,1)