Number Sequence for PO Invoice Voucher

Hi All,

I just want to know where number sequence for ("Purchase, inventory receipt ") and ("Purchase expenditure for product") will be taken in code while we post Purchase Invoice.. i.e Invoice -> voucher -> 5 vouchers will be created and among 5, voucher number sequence for Purchase, inventory receipt and Purchase expenditure for product  , where we have to define in the set up and which class , method is used to pick the Number sequence??

Any help regarding this will be highly appreciated

Thanks and Regards,

Enrique