There are 90 of them that can be formed by concatenation (writing them side-by-side).
You can, of course, form lots more by using mathematical operations. Foe example, 99 = 387,420.489. Combining factorials and powers will give numbers with more than 2 million digits!
There are 34 = 81 numbers.
There are 5 numbers of 1 digit, 25 numbers of 2 digits, and 75 numbers of 3 digits. This makes 105 numbers in all.
6
There are 2000 such numbers.
27
There are 34 = 81 numbers.
6!
There are 5 numbers of 1 digit, 25 numbers of 2 digits, and 75 numbers of 3 digits. This makes 105 numbers in all.
6
256 numbers.
There are 2000 such numbers.
27
pizza
36
125
4*3*2*1 = 24
6*5*4*3*2*1=720 possible numbers