Compress DB by removing unused PRIMARY KEY AUTOINCREMENTAL INTEGER

Using SQLite3 I got following table:

| Idx |  Foo  |   Bar   |
|-----|-------|---------|
|  1  |  It's |something|
|  2  |  and  |  even   |
|  5  |  more |wildcard |

Idx is INTEGER PRIMARY KEY AUTOINCREMENTAL.

As you see Idx 3 and 4 are unused due they got deleted. Can I make these Idx usable again?

I'm not very firm with SQL but afaik, I need autoincremental to identify the row without a doubt, every other column could have doublets.