largest_9dig_prime.py

def is_prime(n):
    if n == 1:
        return False

    i = 2
    while i*i <= n:
        if n % i == 0:
            return False
        i += 1
    return True

c = 0

for i in range(99999, 10000, -1):
     x = str(i)
     x+= x[-2::-1]
     x = int(x)
     if is_prime(x):
             c+=1
             print(x)
             if c >= 3:
                 exit()