You can't use SETI@home for proof of work. The work target has to somehow involve a fully random process.
Lots of very smart people have tried this and failed. The best effort so far has been to find prime numbers, and even that turned out to not be a robust proof of work.
Lots of very smart people have tried this and failed. The best effort so far has been to find prime numbers, and even that turned out to not be a robust proof of work.