1015 Reversible Primes (20 分)
A reversible prime in any number system is a prime whose “reverse” in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (<10^5) and D (1<D≤10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:
The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:
For each test case, print in one line Yes if N is a reversible prime with radix D, or No if not.

Sample Input:
73 10
23 2
23 10
-2
Sample Output:
Yes
Yes
No

解法

这题没啥好说的，最后一个测试点测的是检查原数字本身是不是素数！！！！看清楚定义！！！

from math import sqrt
def isp(n):
    if n < 2: return False
    for i in range(2, int(sqrt(n)) + 1):
        if n % i == 0: return False
    return True

def convert(n, r):
    ans = ''
    while n > 0:
        ans += str(n % r)
        n //= r
    return ans
    
while True:
    n = input().split()
    if len(n) == 1: exit(0)
    num, r = [int(i) for i in n]
    if num < 0: exit(0)
    y = int(convert(num, r), r)
    if isp(num) and isp(y): print("Yes")
    else: print("No")