Using the digits 0 to 9, with no number repeating itself, 151,200 possible combinations of six digits. However, if a true number is required, meaning 0 cannot be the first digit, only 136,080 combinations are available.
Using the digits 1 to 9, with none repeating, 60,480 combinations can be made. To determine the number of combinations, find the number of digits possible for each position and then multiply these numbers. For example, using only numbers 1 to 6 would give the equation 6 x 5 x 4 x 3 x 2 x 1 (also known as 6! or 6 factorial) for a result of 720.