Undecation is the 11th hyperoperation, which is equal to \(a \uparrow^{9} b\) in Knuth's up-arrow notation.[1](dead link)

The n undecated to m is n decated to n decated to ... decated to n (m n's).

Undecation can be written in BEAF as \(\{a,b,9\}\), in chained arrow notation as \(a \rightarrow b \rightarrow 9\) and in Hyper-E notation as E(a)1#1#1#1#1#1#1#1#b.

Undecational growth rate is comparable to \(f_{10}(n)\) in the fast-growing hierarchy.

Cloudy176 called it Hendecation in his faketest F page.[2]


n undecated to 2 = \(a \uparrow^{9} 2\) = \(a \uparrow^{8} a\)


See also

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