Engine number
WARNING: This page is about a different car, the 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
The engine number ("Engine code" and "Serial number") can be found on the rear left of the cylinder block.
Additionally there is a sticker on the toothed belt guard giving the "Engine code" and "Serial number".
The engine code is also given on the vehicle data sticker.
NOTE:
The engine code is also stamped on the front lifting eye (visible when engine cover panel is removed).