Find the biggest prime factor of a number.

sahil-prime.py

# I have a number n
# Test divisinility by numbers in the range 2, Sqrt(n)
# If n is divisible by a prime p, for the first time, keep on dividing it with p till you find the largets power of p that divides n.
# Replace n by n/(p**alpha)
# Repeat the process until I get n = 1 or 
# Print p
from math import ceil

subject = 600851475143
answer = 0

while subject > 1:
  for index in range(2, ceil(subject ** 0.5)):
    if subject % index == 0:
      answer = index

      while subject % index == 0:
        subject /= index
  else:
    answer = subject
    break

print(answer)