Making a list with blanks?

I was wondering if it's possible to do this.. Say I have a row of random numbers (and they're in numerical order, but there are just numbers missing). I want to insert empty rows whenever I'm missing a number.

So for example my list looks like this:
1
4
5
8

But I want it to look like this:
1
(blank)
(blank)
4
5
(blank)
(blank)
8

Any help would be appreciated, thanks!