Heptation or septation refers to the 7th hyperoperation. It is equal to \(a \uparrow\uparrow\uparrow\uparrow\uparrow b\) in Knuth's up-arrow notation. Heptation can be written in array notation as \(\{a,b,5\}\), in chained arrow notation as \(a ightarrow b ightarrow 5\) and in Hyper-E notation as E(a)1#1#1#1#b. Heptational growth rate is equivalent to \(f_6(n)\) in the fast-growing hierarchy.