“three up arrow up arrow up arrow three”
ETA: The notation is called Knuth’s up-arrow notation, and is usually written with up-arrows instead of carets.
Alternatively, “three triple up-arrow three”
“three up arrow up arrow up arrow three”
ETA: The notation is called Knuth’s up-arrow notation, and is usually written with up-arrows instead of carets.
Alternatively, “three triple up-arrow three”