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The tethrapeton (also called tethrapenteract) is equal to E100#^^(#^#)5 = E100#^^(#^5)100 = E100#^^#####100 in Extended Cascading-E Notation.[1] The term was coined by Sbiis Saibian.


The name of this number is based on the number tethrathoth and the root "peton" from "polypeton". Polypeton is the name for a 6-dimensional figure and 6-D figures are constructed from multiple 5-D figures (hence the "poly"), so a "peton" can be considered a 5-dimensional figure.

Approximations in other notations

Notation Approximation
BEAF \(X \uparrow^6 101\ \&\ 100\)
Bird's array notation \(\{100,6 [1 [2 \neg 2] 2] 2\}\)
Hyperfactorial array notation \(100![1] w/8\)
Fast-growing hierarchy \(f_{\varphi(5,0)}(99)\)
Hardy hierarchy \(H_{\varphi(5,0)}(100)\)
Slow-growing hierarchy \(g_{\vartheta(\varphi(5,\Omega+1))}(100)\)


  1. Saibian, Sbiis. 4.3.7 - Extended Cascading-E Numbers Part I. Retrieved 2016-12-19.