Grand terrible tethrathoth is equal to E100(#^^#)^^#100#2 using Extended Cascading-E Notation.[1] The term was coined by Sbiis Saibian.


The name of this number is based on the prefix "terrible" and the number "tethrathoth".

Approximations in other notations

Notation Approximation
BEAF \(\{100,3,2 (X \uparrow\uparrow (2X)) 2\}\)[2]
Bird's array notation \(\{100,3,2 [1 \backslash 3] 2\}\)
X-Sequence Hyper-Exponential Notation \(100\{(X\uparrow\uparrow X)\uparrow\uparrow X\}100\)
Fast-growing hierarchy \(f_{\varepsilon_1}^2(100)\)
Hardy hierarchy \(H_{\varepsilon_1 2}(100)\)
Slow-growing hierarchy \(g_{\vartheta(\varepsilon_{\Omega 2 + \vartheta(\varepsilon_{\Omega 2 + 1})})}(100)\)


  1. Saibian, Sbiis. 4.3.7 Extended Cascading-E Numbers Part IOne to Infinity. Retrieved 2017-02-17.
  2. Using particular notation \(\{a,b (A) 2\} = A\ \&\ a\) with prime b.
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