Invoice Order number

Hi i'm Francesco,
i need an help
I need to manage my invoices,
This is the point

My invoice number needs to be crescential (from 1 to infinte), and it is ok, but, if a order is not paid i don't need to create the invoice.

EXPLANATION

Order #3, Invoice #3: Order #3 is not paid so the Order #4 need to have Invoice #3

NopCommerce 2.65 NoSourceCode.

Thanks for your help
Francesco