Succession, , is the most basic operation; while addition () is a primary operation, for addition of natural numbers it can be thought of as a chained succession of successors of ; multiplication ) is also a primary operation, though for natural numbers it can analogously be thought of as a chained addition involving numbers of . Exponentiation can be thought of as a chained multiplication involving numbers of and tetration (formula_10) as a chained power involving numbers . Each of the operations above are defined by iterating the previous one; however, unlike the operations before it, tetration is not an elementary function.