First digit can be any of the 4 numbers, second can be any of the unused three etc so 4 x 3 x 2 x 1 = 24 different numbers.
Chat with our AI personalities
256
975
0.0588
The answer is 3*3*2*1 = 18. If the leading digit is 0 it is not a 4-digit number.
73 is the largest two-digit number that is prime and has prime numbers for both of its digits.