As mentioned by , only the ESXi hosts are licensed by CPUs/sockets. vCenter Server itself is licensed per instance. So if you are going to manage all hosts from a single vCenter Server you'd need one license for vCenter Server plus the appropriate amount of CPU licenses for the hosts.
Hint: If you are new to VMware, you may initially purchase an Acceleration Kit which contains one license for vCenter Server as well as 6 CPU licenses.
André