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Googology Wiki

The tethrennon is equal to E100#^^#^#9 = E100#^^#########100 in Extended Cascading-E Notation.[1] The term was coined by Sbiis Saibian. Tethrennon is comparable to Bowers' tridecatrix using non-climbing method.


The name of this number is based on the number tethrathoth and the root "xennon" from "polyxennon". Polyxennon is the name for a 10-dimensional figure and 10-D figures are constructed from multiple 9-D figures (hence the "poly"), so a "xennon" can be considered a 9-dimensional figure.

Approximations in other notations

Notation Approximation
BEAF \(X \uparrow\uparrow X^{9}\ \&\ 100\)
Bird's array notation \(\{100,10 [1 [2 \neg 2] 2] 2\}\)
Hyperfactorial array notation \(100![1] w/12\)
Fast-growing hierarchy \(f_{\varphi(9,0)}(99)\)
Hardy hierarchy \(H_{\varphi(9,0)}(100)\)
Slow-growing hierarchy \(g_{\vartheta(\varphi(9,\Omega+1))}(100)\)


  1. Saibian, Sbiis. 4.3.3 - Forging Extended Cascading-E Numbers Part I. Retrieved May 6, 2014.