Doevigintation refers to the 22nd hyperoperation. It is equal to \(a \uparrow^{20} b\), using Knuth's up-arrow notation. Doevigintation can be written in array notation as \(\{a,b,20\}\), in chained arrow notation as \(a ightarrow b ightarrow 20\) and in Hyper-E notation as E(a)1#1#1#1...1#1#1#b (19 ones). Doevigintational growth rate is equivalent to \(f_{21}(b)\) in the fast-growing hierarchy.