How many combinations can you make with three numbers?

You can make 6 combinations with 3 numbers. They are:

123 213 312

132 231 321

* * * * *

NO! Those are permutations! In combitorials, the order does not matter so that the combination 123 is the same as the combination 132 etc. So all of the above comprise just 1 combination.

With three numbers you can have

1 combination of three numbers (as discussed above),

3 combinations of 2 numbers (12, 13 and 23)

3 combinations of 1 number (1, 2 and 3)

In all, with n numbers you can have 2n - 1 combinations. Or, if you allow the null combination (that consisting of no numbers) you have 2n combinations.