It is hard to determine a person that has a number tied to their name, unless you know what the numbers stand for. The numbers 123456789 could be an id number for someone in the government or a persons id number in witness protection.

you count how many numbers there are and then divide it or count one from each side until you get an answer. 123456789 middle is 5 1234567890 midlle is 5 and a half.

If the numbers are not allowed to repeat themselves then 362,880. * * * * * That is the number of permutations, not combinations. In a combination the order of the digits does not matter. So there is only one 9-digit combination.