How many 4 digit combination no repeated numbers?

In decimal, 4 digits ( 0 - 9) you can represent any number from 0000 to 9999. That is 10,000 unique number combinations. Incidentally, the number of unique cominations is 10 to the 4th power. In binary, 4 digits (0 - 1) can represent 16 different cominations from 0000 - 1111. This is given by 2 to the 4th power