User blog comment:ANDY3556/Andrew's A-Notation/@comment-31966679-20180611224715

Pretty good but you could generalize this and make it faster-growing:

\(A(x, y) = x ^ y\)

\(A(a, b, ..., 1) = A(a, b, ...)\)

\(A(a, b, ..., c) = A(a, b, ..., A(a, b, ..., c - 1))\)

Then you could diagonalize and extend it further, but I'm not gonna get into that.