User blog comment:Nayuta Ito/Extended extended chain notation/@comment-223.255.230.236-20141219104455/@comment-1605058-20141219191732

I'm quite sure $$K\xrightarrow[K]{}K$$, where K is half of Loader's number, will do.

Okay, but putting all of this "cheating" aside, you won't get anywhere near Loader's number using this notation if you limit yourself to, say, numbers below 10000 and at most 10000 arrows.