prime-criba.py

n = 20
criba = []

for i in range(n):
	criba.append(True)

def calculate_criba():
	criba[0] = criba[1] = False;
	for i in range(2, n):
		if criba[i] :
			for j in range(i*i, n, i) :
				criba[j] = False

calculate_criba()

print(criba)