Vigintation refers to the 20th hyperoperation starting from addition. It is equal to \(a \uparrow^{18} b\), using Knuth's up-arrow notation. Vigintation can be written in array notation as \(\{a,b,18\}\), in chained arrow notation as \(a ightarrow b ightarrow 18\) and in Hyper-E notation as E(a)1#1#1#1...1#1#1#b (17 ones). Vigintational growth rate is equivalent to \(f_{19}(n)\) in the fast-growing hierarchy.