**Decation** refers to the 10th hyperoperation starting from addition. It is equal to \(a \uparrow^{8}b\), in Knuth's up-arrow notation.^{[1]}

Decation can be written in BEAF and BAN as \(\{a,b,8\}\), in chained arrow notation as \(a \rightarrow b \rightarrow 8\), in the Graham Array Notation as \([a,b,8]\), and in Hyper-E notation as E(a)1#1#1#1#1#1#1#b.

Decational growth rate is equivalent to \(f_9(n)\) in the fast-growing hierarchy.

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