Crivo de Eratóstenes

from numpy import arange, array, hstack, savetxt, sqrt
from sys import argv
n = int(argv[1])
primos = arange(2,n+1)
primos = hstack((array(2), primos[primos%2 == 1]))
for i in arange(3, sqrt(n)+1, 2):
    primos[(i*i-3)/2 + 1::i] = 0
primos = primos[primos!=0]
savetxt('primos', [primos], fmt='%d', delimiter=' ', newline='')