The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.
There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.
How many circular primes are there below one million?
圆周素数
197被称为圆周素数，因为将它逐位旋转所得到的数：197/971和719都是素数。
小于100的圆周素数有十三个：2、3、5、7、11、13、17、31、37、71、73、79和97。
小于一百万的圆周素数有多少个？
import math
def is_Prime(number):
if number < 2:
return False
for x in range(2, int(math.sqrt(number)) + 1):
if number % x == 0:
return False
return True
def get_brothers(number):
result = []
number_level = len(str(number))
for i in range(0, number_level):
result.append(number)
number_str = str(number)
number = eval(number_str[1:] + number_str[0])
return result
count = 0
for i in range(2, 1000001):
if is_Prime(i) and not '0' in str(i):
ok = True
numbers = get_brothers(i)
for n in numbers:
if not is_Prime(n):
ok = False
break
if ok:
count += 1
print i
print "count = %s" % count
感想：
- 一开始审题审错了，居然对着197各种排列组合……