how does one use code to do this:

produce 15 random numbers [EDIT: from 1 - 15] that are not in any order, and that only occur once
eg.

1 4, 2, 5, 3, 6, 8, 7, 9, 10, 13, 12, 15, 14, 11

rand() or arc4rand() can repeat some, which is not what im after. 

Thanks