PUZZLE 073 Number Line-Up

There are some pieces of paper hanging up with numbers on, and one of them is missing.
Which number do you think is written on the missing piece of paper?

Hint 1

There is a rule determining how the numbers are lined up.
See if you can figure out what it is.

Hint 2

It's hard to see how the numbers are lined up if you view them as a whole.
Try splitting them up in a few places.

Hint 3

The '9' can be split off as a separate digit.

Super Hint

Continuing on from hint three...
All of the other numbers have two digits each.

Answer for 'Number Line-Up'

The answer is '2'.