How many servers for a SSAS tabular solution in a prod environment

Hi,

I need to plan the prod infrastructure where deploying a SSAS tabular solution. It could be enough a single server with the SQL Server 2012 engine and the SSAS tabular instance having 40-64 GB as memory?

Or is it better to have 2 servers one for SQL Server engine and the other one for SSAS tabular instance? In this last case, is it enough to have one Enterprise Edition license for both machines?

Thanks