Octation refers to the 8th hyperoperation starting from addition. It is equal to \(a \uparrow\uparrow\uparrow\uparrow\uparrow\uparrow b\) in Knuth's up-arrow notation Octation can be written in array notation as \(\{a,b,6\}\), in chained arrow notation as \(a ightarrow b ightarrow 6\) and in Hyper-E notation as E(a)1#1#1#1#1#b. Octational growth rate is equivalent to \(f_7(n)\) in the fast-growing hierarchy.