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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]

## Examples

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