An inverse of the up arrow notation defined by

			(1)
			(2)
			(3)

where is the number of times the natural logarithm must be iterated to obtain a value .

Vardi, I. Computational Recreations in Mathematica. Redwood City, CA: Addison-Wesley, pp. 12 and 231-232, 1991.

CITE THIS AS:

Weisstein, Eric W. "Down Arrow Notation." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/DownArrowNotation.html