title: Generate non-repeating, no sequential numbers
body: <p>how does one use code to do this:</p>
  
  <p>produce 15 random numbers [EDIT: from 1 - 15] that are not in any order, and that only occur once
  eg.</p>
  
  <p>1 4, 2, 5, 3, 6, 8, 7, 9, 10, 13, 12, 15, 14, 11</p>
  
  <p>rand() or arc4rand() can repeat some, which is not what im after. </p>
  
  <p>Thanks</p>