It's practically impossible to crack SHA-256. You think you can crack that? Good bloody luck. And you can't use an encrypted seed, if that's what you mean. It's encrypted in such a way that the encrypted form has no direct correlation to the unencrypted form whatsoever besides the encryption key.
Edit: NO I don't think I can crack it; but this way that I do sort of avoids the dangers of repitition as you're not relying on yourself you're relying on what numbers are in the SHA-256 encryption. I'm not saying that I can decrypt it everyone knows that's impossible.