<P> In mathematics, Knuth's up - arrow notation is a method of notation for very large integers, introduced by Donald Knuth in 1976 . It is closely related to the Ackermann function and especially to the hyperoperation sequence . The idea is based on the fact that multiplication can be viewed as iterated addition and exponentiation as iterated multiplication . Continuing in this manner leads to tetration (iterated exponentiation) and to the remainder of the hyperoperation sequence, which is commonly denoted using Knuth arrow notation . This notation allows for a simple description of numbers far larger than can be explicitly written out . </P> <P> A single arrow means exponentiation (iterated multiplication), more than one arrow means iterating the operation associated with one less arrow . </P> <P> For example: </P>

What does an upward arrow mean in math