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.


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 \(X \uparrow^{10} 101\ \&\ 100\)
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.
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