As ppl pointed out , license is based on socket and not core ... So if you have a dual socket system , you will need 2 licenses ... If you have quad socket system , you will need 4 licenses . The underlying cores does not count .
For example , Dual cpu ( single core or dual core or quad core ) all require 2 licenses . In the same manner Quad cpu ( single core or dual core or quad core ) require 4 licenses .
Hope this helps .