Hexation or sextation refers to the 6th hyperoperation starting from addition. It is equal to \(a \uparrow\uparrow\uparrow\uparrow b\) in Knuth's up-arrow notation. Sunir Shah uses the notation \(a **\ b\) to indicate this. Jonathan Bowers calls it 'a to the b'th layer'. Sbiis Saibian proposes the notation \(a_{ightarrow b}\) in analogy to ba for tetration, but he usually uses up-arrows. Hexation can be written in array notation as \(\{a,b,4\}\), in chained arrow notation as \(a ightarrow b ightarrow 4\) and in Hyper-E notation as E(a)1#1#1#b.