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

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

why does mine take too long to produce an answer.... I tried it with smaller numbers and it seems to work. I would really appreciate the help as i dont understand what makes your code so much smoother than mine (besides the fact its shorter.

def isitprime(n):
k=2
while k<n/2:
if n%k!=0:
pass
else:
k="not prime"
break
k= k+1
if k!="not prime":
k="PRIME"
else:
k="NOT PRIME"
return k

def getprimefactors(n):
bigprime=0
k=n/2
while k>0:
if n%k==0:
a=n/k
if isitprime(a)=="PRIME" and a>bigprime:
bigprime=a
else:
pass
else: pass
k=k-1
print bigprime

print isitprime(6023)
getprimefactors(6023)