PEP3 | Python Fiddle

# The prime factors of 13195 are 5, 7, 13 and 29.
# What is the largest prime factor of the number 600851475143 ?
# source for formula: https://primes.utm.edu/prove/merged.html
# the Sieve of Eratosthenes (ca 240 BC):

from math import sqrt
myNumber = int(raw_input("Enter a number to find its largest prime factor: "))
print "%s" %myNumber

#make a list of all the integers less than or equal to myNumber
myIntegers = []
i = 2
while i <= myNumber:
    myIntegers.append(i)
    i += 1

#find square root of myNumber
myNumberSquared = sqrt(myNumber)

#strike out multiples of all prime numbers less than or equal to the square root of myNumber
count = 0
prime = myIntegers[0]
while len(myIntegers) > 1 and myIntegers[0] <= myNumberSquared:
    for index, item in enumerate(myIntegers):
        if myIntegers[index] % prime == 0:
            del myIntegers[index]
        count += 1  
    prime = myIntegers[0]
# print count

#get the largest prime number
largest_prime_factor = myIntegers[-1]
print "The largest prime factor of ", myNumber, " is ", largest_prime_factor

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