Added Problem 3

Problem_3.py

@@ -0,0 +1,25 @@
+######################################################################
+# The prime factors of 13195 are 5, 7, 13 and 29.
+#
+# What is the largest prime factor of the number 600851475143 ?
+#
+######################################################################
+
+primes = [1]
+original = 600851475143
+
+for x in range(1, int(original / 2)):
+    print(x)
+    tester = 600851475143
+    for prime in primes:
+        tester /= prime
+
+    if x > tester:
+        break
+
+    if int(original) % x is 0:
+        primes.append(x)
+        original /= x
+
+print("{}".format(primes))
+# Solution: 6857