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Tethrato-tethrathoth (also called tethrarxitri) is equal to E100#^^#^^#100 in Extended Cascading-E Notation.[1] The term was coined by Sbiis Saibian. This number belongs to the tethratope regiment.


The name "tethrato-tethrathoth" is based on the "tethrato-" operator and tethrathoth.

The name "tethrarxitri" is based on the number tethrathoth, "arx-" meaning "citadel" in Latin, and "tri" meaning three.


It is likely pronounced as so:

Approximations in other notations

Notation Approximation
BEAF \(X \uparrow\uparrow\ X \uparrow\uparrow\ X \&\ 100\)
Bird's array notation \(\{100,101 [1 [1 \backslash 2 \neg 2] 2] 2\}\)
Hyperfactorial array notation \(100![1] w/[1,1,1,1,1,1,2]\)
Fast-growing hierarchy \(f_{\varphi(\varepsilon_0,0)}(99)\)
Hardy hierarchy \(H_{\varphi(\varepsilon_0,0)}(100)\)
Slow-growing hierarchy \(g_{\vartheta(\vartheta_1(\varepsilon_{\Omega+1}))}(100)\)


  1. Saibian, Sbiis. 4.3.9 - Forging Extended Cascading-E Numbers Part III. Retrieved Jan 13, 2018.