Enneation or nonation refers to the 9th hyperoperation starting from addition. It is equal to \(a \uparrow^{7}b\) in Knuth's up-arrow notation. Enneation can be written in array notation as \(\{a,b,7\}\), in chained arrow notation as \(a ightarrow b ightarrow 7\) and in Hyper-E notation as E(a)1#1#1#1#1#1#b. Enneational growth rate is equivalent to \(f_8(n)\) in the fast-growing hierarchy.