def multipli(n,b):
    	c = []
	x = n
	i = 1
	while x<=b:
		c[0:0]=[x]
		i = i+1
		x = i*n
	return set(c)

def eratostene(nmax):
        L = set(range(3,nmax+1,2))
	c =set([])
	while len(L)>0:
		k = min(L)
		c.add(k)
		L = L - multipli(k,nmax)
	return c