Is there a biggest number?

A googolplex is a huge number that can be expressed compactly because of nested exponentiation. Other procedures (like tetration) can express large numbers even more compactly. The natural question is: what procedure uses the smallest number of symbols to express the biggest number? A Turing machine formalizes the notion of a procedure, and a busy beaver is the Turing machine of size n that can write down the biggest possible number . The bigger n is, the more complex the busy beaver, hence the bigger the number it can write down. For n=1, 2, 3, 4 and 5 the numbers expressible are not huge, but research as of 2006 shows that for n=6 the busy beaver can write down a number at least as big as . It is an open question whether the seventh busy beaver can express a googolplex.