Is Hashgraph patented?
No, the Hashgraph mathematical proof itself is not patented, because only inventions can be patented, not the science itself as the mathematical proof. Swirlds own the US Patent_9,646,029_B1 claiming a distributed database system that reaches consensus with a proof of stake model and the Hashgraph algorithm. Swirlds have filed the patent in the US and Australia.
The patent application got refusal in Korea and has chosen not to continue the national phase in Germany (EU).
Tagion used the math behind Hashgraph in a completely different way, in a different context, which is its P2P distributed database technology. Tagion as well filed patents in EU, that are related to the gossip and security mechanisms and the database technology.