Auto Generated Number Field with prefix

Auto Generated Number Field with prefix

Any help will be appreciated:
Issue
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The Auto Number starts from "1" -  It is missing the following basic abilities:
1- No Prefix can be set For Example Starting with a letter
2- No starting Number - I want to start the first record from 2500+ 2501, 2502.. (Is this too much to ask??)
3- No Leading Zero possible - for example 000001, 000002...
I need to create an auto numbered field for item lot number looking like this L0000001, L0000002, L0000003....L0000015...

I used a formula field that adds "L" + another_auto_number_field , but all I get is L1, L2, L3...

Does anyone know how to do this please!
Regards
Reza