Tetration

In mathematics, tetration (or hyper-4) is the next hyperoperation after exponentiation, and is defined as iterated exponentiation. The word was coined by Reuben Louis Goodstein, from tetra- (four) and iteration. Tetration is used for the notation of very large numbers. Shown here are the first four hyperoperations, with tetration as the fourth (and succession, the unary operation denoted taking and yielding the number after , as the 0th):