Just another update

Task/Factors-of-an-integer/Python/factors-of-an-integer-4.py

@@ -1,13 +1,18 @@
-def factor(n):
-	a, r = 1, [1]
-	while a * a < n:
-		a += 1
-		if n % a: continue
-		b, f = 1, []
-		while n % a == 0:
-			n //= a
-			b *= a
-			f += [i * b for i in r]
-		r += f
-	if n > 1: r += [i * n for i in r]
-	return r
+from itertools import chain, cycle, accumulate # last of which is Python 3 only
+
+def factors(n):
+    def prime_powers(n):
+        # c goes through 2, 3, 5, then the infinite (6n+1, 6n+5) series
+        for c in accumulate(chain([2, 1, 2], cycle([2,4]))):
+            if c*c > n: break
+            if n%c: continue
+            d,p = (), c
+            while not n%c:
+                n,p,d = n//c, p*c, d + (p,)
+            yield(d)
+        if n > 1: yield((n,))
+
+    r = [1]
+    for e in prime_powers(n):
+        r += [a*b for a in r for b in e]
+    return r