fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364140 .. there are also invalid public keys. The reason is there are pub keys that lie outside the curve. But i gotta agree that the mentioned pubs above are interesting, especially knowing that one of their addresses is a used one.
There is no such a thing as invalid private or public key, whatever private key you think is invalid or outside the range, I will prove you wrong if you just show it to me.
About the keys above, here are 2 private keys, one will open one of the above, I just changed the X on the original one it converted to it's mirror version.
7fffffffffffffffffffffffffffffff5d576e7357a4501ddfe92f46681b20a0
If you have seen the start range, end range for bitcoin keys, the above is the middle range.😉