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Icosalogue
100000.....00000    19

100000.....00000

100000.....00000
100000.....00000
10000000000
Icosalogue in zeroes

The icosalogue is equal to E1#20, using Hyper-E notation.[1] The term was coined by Sbiis Saibian. In up-arrow notation it can be written $$10 \uparrow\uparrow 20$$.

This number is also called existron.[2]

## Contents

### Etymology

The name of this number is based on Greek prefix "icosa-", another term for 20 and the word "logarithm".

### Approximations in other notations

Notation Approximation
Up-arrow notation $$10 \uparrow\uparrow 20$$ (exact)
Chained arrow notation $$10 \rightarrow 20 \rightarrow 2$$ (exact)
BEAF $$\{10,20,2\}$$ (exact)
Hyperfactorial array notation $$22!1$$
Fast-growing hierarchy $$f_3(19)$$
Hardy hierarchy $$H_{(\omega^2) 19}(28)$$
Slow-growing hierarchy $$g_{\epsilon_0}(20)$$