Enneadecation refers to the 19th hyperoperation starting from addition. It is equal to \(a \uparrow^{17} b\) in Knuth's up-arrow notation.

Enneadecation can be written in array notation as \(\{a,b,17\}\) and in chained arrow notation as \(a \rightarrow b \rightarrow 17\).

Enneadecational growth rate is equivalent to \(f_18(n)\) in the fast-growing hierarchy.

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