Would 200 or 2000 work for you?
No offence, but whatever that number is, it is absolutely irrelevant simply because in the cluster world 1+1 != 2, so until you specify some details on what r u trying to accomplish I say pick your favorite number and go with it.
The highest number of nodes I know of is 90. That customer (a large telco in the US) was even targetting going to 160 nodes. That's JBoss nodes in a cluster.