How many sets of 6 numbers can be formed using 3 digits?

Answer 1

Your question was a little unclear in two ways:

You said "using 3 digits". Are 1 and 2 digit numbers allowed?

and

If you reorder the numbers in a set, do you count it twice? For instance, if you had already counted the set 101, 102, 103, 104, 105, 106, would you also count 106, 105, 104, 103, 102, 101?

If yes to both questions, there are 985,084,775,273,880,000 different sets.

If yes to the first question, no to the second, there are 1,368,173,298,991,500 different sets.

If no to the first question, yes to the second, there are 522,639,254,696,832,000 different sets.

If no to both questions, there are 725,887,853,745,600 different sets.

Hope this helped :).