Graham’s number is truly, absolutely staggering…
erratum: Graham’s number is an upper bound for a problem in Ramsey theory. We erroneously stated that the problem was eventually solved, and the actual answer was six. No, six was proven to be a lower bound.
From the Wikipedia article:
Although the solution to this problem is not yet known, Graham’s number is the smallest known upper bound. This bound was found by Graham and B. L. Rothschild (see (GR), corollary 12). They also provided the lower bound 6, adding the qualified understatement: “Clearly, there is some room for improvement here.”