Código Python:
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def factor(n): """return a list with the prime factors of n. Complexity: O(sqrt(n))""" l = [] #List of factors i = 2 while i * i <= n: #From 2 to sqrt(n) while n % i == 0: #While i is factor of n, add to the list of factors. l.append(i) n /= i i += 1 if n != 1: #If n isn't 1, then is a factor. l.append(n) return l for i in range(2, 21): print i, "->", factor(i)