Which number do you think is written on the missing piece of paper?
There is a rule determining how the numbers are lined up.
See if you can figure out what it is.
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.
The '9' can be split off as a separate digit.
Continuing on from hint three...
All of the other numbers have two digits each.
The answer is '2'.