projecteuler_prob_3.py

a=600851475143 
i=2

while i<a :
    if a%i==0:
        a1=a/i
    else :
        i+=1
        continue
    n=2
    while n<a1:
        if a1%n==0 :
            break
        n+=1
    if n==a1:
        break
    i+=1
print a1