User blog comment:Kochab1/I love numberphile/@comment-32783837-20171022200045

It was inevitable, what with the thousands of requests they were getting.

Now, instead of people trying to ridiculously extend Graham's number, we'll start seeing stuff like "how about TREE(TREE(TREE(TREE(...(TREE(TREE(TREE(Graham's number))))...))) with TREE(Graham's number) nested TREEs"