Procurement lot sizing question

Hi,

I have a question regarding procurement lot sizing  (purchasing of raw materials)

I would like to condition lot size on number of demands that triger procurement.

For example:

If I would have one demand of 1000 I would want for system to create purchase requisition for  2500 pcs.

If I would have two demands for 1000 I would want a purchase requisition for  5000

If I would have one demand for 2000 I would want for system to create purchase requisition for 4000

Is this possible in basic functionality of SAP

Thanks for your help

Nejko