#求素數
#素數：只能被1和它自己整除
n = int(input('Please input a number >>>'))
flag = False
for i in range(2,n):
    if n % i == 0:   #找到條件是什麼
        flag = True
        print(i)
        break
if flag:
    print(n,'is not a prime number.')
else:
    print(n,'is a prime number.')

2、或者如下：

#求素數
#素數：只能被1和它自己整除
 

n = int(input('Please input a number >>>'))
flag = False
for i in range(2,n):
    if n % i == 0:   #找到條件是什麼
        print(n,'is not a prime number.')
        break
else:
    print(n,'is a prime number.')

 3、或者如下：

#求素數
#正向思維，能被1 和本身整除
#
n = int(input('Please input a number: '))
i  
 
= 0

for m in range(1,n+1):
    if n%m == 0:
        i += m
if i == (1+n):
    print(n,'is a prime number.')
else:
    print(n,'is not a prime number.')