permutations of a number ( digits in it) to print the biggest prime number formed with it

permutations_prime.py

d = []

def isprime(n):
    if n<=1:    return False
    if n<=3:    return True
    if n%2 == 0 or n%3 == 0:    return False
    i = 5
    while i*i <= n:
        if n % i ==0 or n%(i+2) == 0:   return False
        i+=1
    return True

def permutations(s, taken, current):
    if bin(taken)[2:].count('1') == len(s):
        if isprime(int(current)):
            d.append(current)
    for i in range(len(s)):
        if (taken & (1 << i)):  continue
        temp = current
        temp += s[i]
        new_taken = taken | (1 << i)
        permutations(s, new_taken, temp)
            
s = '4691'
permutations(s, 0, '')
print(d, max(d))