How many database licenses do we need for setting 2 servers (nodes) into a cluster?

Question

Suppose we have a server that has only 1 CPU with 1 core, so we need 1 Oracle database license for installing a database into it. Now, if we would need to add a second server, combine them into cluster and install database into it, then how many licenses do we need - 2 database licenses and 1 Clusterware licenses or 1 database license and 1 cluster license? I'm not sure, how Oracle treats joined into Oracle cluster servers - as one server or still as separate servers? Because we would need to buy expensive Oracle cluster software, then it would be logical for Oracle to treat joined servers as one.