Sorry @LSOC but I'm pretty sure that Invoices & Credit Notes use the same sequence.
I'm pretty sure that's how QB Desktop worked too (it's been a while) so I've always just put a "C" behind the number to denote a Credit.
Be careful with that though ... if you add a "C" behind your credit note numbers, the next time you open an invoice it will have a "C" behind the invoice number which will need to be deleted.
Hope this helps.