Why doesn't it decode the entire message?

Question

Python

import base64

num = 0
count = 0
cipher_b64 = b"MTAwLDExMSwxMDAsOTYsMTEyLDIxLDIwOSwxNjYsMjE2LDE0MCwzMzAsMzE4LDMyMSw3MDIyMSw3MDQxNCw3MDU0NCw3MTQxNCw3MTgxMCw3MjIxMSw3MjgyNyw3MzAwMCw3MzMxOSw3MzcyMiw3NDA4OCw3NDY0Myw3NTU0MiwxMDAyOTAzLDEwMDgwOTQsMTAyMjA4OSwxMDI4MTA0LDEwMzUzMzcsMTA0MzQ0OCwxMDU1NTg3LDEwNjI1NDEsMTA2NTcxNSwxMDc0NzQ5LDEwODI4NDQsMTA4NTY5NiwxMDkyOTY2LDEwOTQwMDA="


def a(num):
    if (num > 1):
        for i in range(2, num):
            if (num % i) == 0:
                return False
                break
        return True
    else:
        return False


def b(num):
    my_str = str(num)
    rev_str = reversed(my_str)
    if list(my_str) == list(rev_str):
        return True
    else:
        return False


cipher = base64.b64decode(cipher_b64).decode().split(",")

while (count < len(cipher)):
    if (a(num)):
        if (b(num)):
            print(chr(int(cipher[count]) ^ num), end='', flush=True)
            count += 1
            if (count == 13):
                num = 500000
            if (count == 26):
                num = 5000000

    else:
        pass
    num += 1

print()