输出1-20之间的所有素数

# 输出1-20之间的所有素数
res = []
mark = 0
for i in range(2,20):
    for j in range(2,int((i/2)+1)):
        if i % j == 0:
            mark = 1
    if mark == 0:
        res.append(i)
    mark = 0

print(res)   # [2, 3, 5, 7, 11, 13, 17, 19]