User blog comment:Username5243/A UNAN calculator thingy/@comment-27516045-20171110012006/@comment-27516045-20171110112547

Yeah, I must say it is stupid. Your letter notation is far more notable to googology than, say, some random xE^ number. And yet it isn't published anywhere. Things like this should have exceptions to the rules.

As for why those got chosen, I don't know. I'll have to ask the creator of the calculator (which is not me). (I'll probably tell him to keep the Ax = x+1 thing, but he can change the others.)