Down arrow notation is an inverse of the Knuth up-arrow notation defined by
 |  |  |
(1)
|
 |  |  |
(2)
|
 |  |  |
(3)
|
where 
is the number of times the natural logarithm
must be iterated to obtain a value 
.
Down Arrow Notation
See also
Knuth Up-Arrow NotationExplore with Wolfram|Alpha
References
Vardi, I. Computational Recreations in Mathematica. Redwood City, CA: Addison-Wesley, pp. 12 and 231-232, 1991.Referenced on Wolfram|Alpha
Down Arrow NotationCite this as:
Weisstein, Eric W. "Down Arrow Notation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DownArrowNotation.html