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Added comments to the code of the first 5 problems in C.

Python/projecteuler.py

@@ -1,6 +1,6 @@
 #!/usr/bin/python3
 
-from math import sqrt, floor
+from math import sqrt, floor, gcd
 
 from numpy import ndarray, zeros
 
@@ -19,12 +19,6 @@ def is_prime(num):
 
     return True
 
-def gcd(a, b):
-    if b == 0:
-        return a
-
-    return gcd(b, a%b)
-
 def lcm(a, b):
     return a * b // gcd(a, b)