User blog comment:Googleaarex/Hyper-Operators Numbers/@comment-25371339-20140917182428

What about an expansion?

nxundefined= n<<<<...<<>>...>>>> w/ x angle brackets

nn = nn^m

nn<> = nn^^m

nn x  = nn<<<...<<>>...>>> w/ x angle brackets

and so on...

The limit is nn n n ... n<m>