What is wrong with this mod rewrite?

Question

This is my original, working, script. Unless the request is a file that exists you get sent to the index page.

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f [NC]
RewriteRule .* /n/index.php [NC]

Now I want to add in support for variables on a specific page where all the requests will look like this:

abc/def/integer

and i want to grab that integer value and change it to

abc/def?id=integer

So I tried adding this line to my file (right above the other rule) and it doesnt work. And lyxx.com tells me i have an error somewhere. Where would

RewriteRule ^/abc/def/([0-9]+)\$ /n/index.php?id=$1

But