Update math.py

Solve bug in function "prime_sieve"

cyaron/math.py

@@ -226,19 +226,20 @@ def catalan_number(n):
 def prime_sieve(n):
     """
     Return a list of prime numbers from 2 to a prime < n. Very fast (n<10,000,000) in 0.4 sec.
-    
+
     Example:
     >>>prime_sieve(25)
     [2, 3, 5, 7, 11, 13, 17, 19, 23]
 
     Algorithm & Python source: Robert William Hanks
     http://stackoverflow.com/questions/17773352/python-sieve-prime-numbers
     """
-    sieve = [True] * int(n/2)
+    sieve = [True] * (n//2)
     for i in range(3,int(n**0.5)+1,2):
-        if sieve[int(i/2)]:
-            sieve[i*int(i/2)::i] = [False] * (int((n-i*i-1)/(2*i))+1)
-    return [2] + [2*i+1 for i in range(1,int(n/2)) if sieve[i]]
+        if sieve[i//2]:
+            sieve[i*i//2::i] = [False] * ((n-i*i-1)//(2*i)+1)
+    return [2] + [2*i+1 for i in range(1,n//2) if sieve[i]]
+
 
 
 #--- bezout coefficients--------------------------------------------------------------------------