How much four digit numbers can be made with 0 1 2 3

Pretty sure 16. 4 digits each put into a different spot so 4x4 = 16

first digit and second digit and third digit and fourth digit

3 choices x 3 remaining x 2 remaining x 1 remaining = 18

(the first digit has only 3 possibilities because 0 cannot be the first digit)

This is assuming each digit can only be used once.

Answer: 18